<PAGE>
                                                                   EXHIBIT 10.15
                     AMENDMENT NUMBER SEVEN TO AMENDED AND
                      RESTATED LOAN AND SECURITY AGREEMENT


          This AMENDMENT NUMBER SEVEN TO AMENDED AND RESTATED LOAN AND SECURITY
AGREEMENT (this "Amendment") is entered into as of December 12, 1997, by and
between Foothill Capital Corporation, a California corporation ("Foothill"), on
the one hand, and Phoenix Network, Inc., a Delaware corporation ("Phoenix"),
Phoenix Network Acquisition Corp., a Delaware corporation ("PNAC"), and
AmeriConnect, Inc., a Delaware corporation ("AmeriConnect"), on the other hand,
with reference to the following facts:

     A.   Foothill, as lender, and Phoenix, as borrower, heretofore entered into
          that certain Amended and Restated Loan and Security Agreement, dated
          as of September 26, 1995 (despite the fact that the recitals thereof
          erroneously referred to "1993" rather than "1995") (herein the
          "Original Agreement");

     B.   Phoenix and PNAC entered into that certain Amendment Number One to
          Amended and Restated Loan and Security Agreement, dated as of a date
          in October, 1996 (the "First Amendment"), with Foothill, to amend the
          Original Agreement to, among other things, add PNAC as a secured co-
          borrower, and modify the Borrowing Base, in each case as set forth in
          the First Amendment;

     C.   Phoenix, PNAC, and AmeriConnect (individually and collectively,
          jointly and severally, "Borrower") entered into that certain Amendment
          Number Two to Amended and Restated Loan and Security Agreement, dated
          as of December 23, 1996 (the "Second Amendment"), with Foothill, to
          amend the Original Loan Agreement, as previously amended, to, among
          other things, add AmeriConnect as a secured co-borrower, and modify
          the Borrowing Base, in each case as set forth in the Second Amendment;

     D.   Borrower entered into that certain Amendment Number Three to Amended
          and Restated Loan and Security Agreement, dated as of March 12, 1997
          (the "Third Amendment"), with Foothill, to amend the Original Loan
          Agreement, as previously amended, to, among other things, provide for
          a $2,000,000 bridge loan to Borrower, provide for a reducing
          Overadvance to Borrower, change certain pricing with respect to the
          credit facilities under the Agreement, provide for the issuance of the
          Warrants to Foothill, and modify the Borrowing Base, in each case as
          set forth in the Third Amendment;

     E.   Borrower entered into that certain Amendment Number Four to Amended
          and Restated Loan and Security Agreement, dated as of March 28, 1997
          (the 
<PAGE>
 
          "Fourth Amendment"), with Foothill, to amend the Original Loan
          Agreement, as previously amended, to, among other things, provide for
          the restatement of certain covenants, the elimination of certain
          covenants, the addition of certain covenants, and the waiver of
          certain described Events of Default that existed as of March 28, 1997,
          prior to the effectiveness of the Fourth Amendment, in each case as
          set forth in the Fourth Amendment;

     F.   Borrower entered into that certain Amendment Number Six to Amended and
          Restated Loan and Security Agreement, dated as of September 1, 1997
          (the "Sixth Amendment"), with Foothill, to amend the Original Loan
          Agreement, as previously amended, to, among other things, provide for
          (i) an extension of, and certain other modifications in respect of,
          the Permitted Overadvance Amount and (ii) a temporary principal
          moratorium in respect of the Bridge Loan, in each case as set forth in
          the Sixth Amendment (the Original Agreement, as amended by the First
          Amendment, by the Second Amendment, by the Third Amendment, by the
          Fourth Amendment, and by the Sixth Amendment, is referred to herein as
          the "Agreement");

     G.   Borrower originally intended to enter into that certain Amendment
          Number Five to Amended and Restated Loan and Security Agreement, dated
          as of July __, 1997 (the "Fifth Amendment"), with Foothill, to amend
          the Original Loan Agreement, as previously amended, to, among other
          things, provide for certain consents and amendments in connection with
          a contemplated transaction between Phoenix and Sprint Communications
          or its Affiliates (collectively, "Sprint").  Inasmuch as Sprint no
          longer intends to enter into that contemplated transaction with
          Borrower, Borrower no longer intends to enter into the Fifth Amendment
          with Foothill and has requested Foothill to amend the Agreement to,
          among other things, delete references therein to the Fifth Amendment
          and certain documents (including the "Sprint Subordination Agreement")
          contemplated therein;

     H.   Borrower (1) has advised Foothill that Borrower currently is engaged
          in discussions with certain prospective purchasers relative to the
          acquisition of Borrower by one or more of such prospective purchasers,
          (2) has discussed with Foothill the expected timetable of the proposed
          acquisition, and (3) has requested Foothill to provide certain
          additional working capital financing to Borrower during part or all of
          period covered by the expected timetable;

     I.   Borrower has requested Foothill to further amend the Agreement to,
          among other things, change certain pricing with respect to the credit
          facilities under the Agreement, provide for an additional bridge loan,
          and extend the maturity 

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          date of the bridge loans and the permitted overadvance facility, in
          each case, as set forth in this Amendment;

     J.   Based in part on the mutual expectations of Borrower and Foothill
          regarding the timetable for the aforementioned proposed acquisition,
          Foothill is willing to so amend the Agreement in accordance with the
          terms and conditions hereof; and

     K.   All capitalized terms used herein and not defined herein shall have
          the meanings ascribed to them in the Agreement, as amended hereby.

          NOW, THEREFORE, in consideration of the above recitals and the mutual
promises contained herein, Foothill and Borrower hereby agree as follows:

          1.    Amendments to the Agreement.
                --------------------------- 

                a.   Section 1.1 of the Agreement hereby is amended by
                     -----------                                      
adding the following new defined terms in alphabetical order:

                "Definitive Purchase Agreement" means a definitive purchase and
                 -----------------------------                                 
     sale agreement or merger agreement, on terms and conditions reasonably
     satisfactory to Foothill, for the acquisition by Prospective Purchaser of
     Borrower.

                "Definitive Purchase Agreement Condition" means the receipt by
                 ---------------------------------------                      
     Foothill, on or before January 1, 1998, of evidence satisfactory to
     Foothill that: (a) Borrower and a purchaser reasonably satisfactory to
     Foothill ("Prospective Purchaser") have entered into the Definitive
     Purchase Agreement; and (b) the Definitive Purchase Agreement is in full
     force and effect.

                "Prospective Purchaser" has the meaning set forth in the
                 ---------------------                                  
     definition of `Definitive Purchase Agreement.'

                "Seventh Amendment" means that certain Amendment Number Seven to
                 -----------------                                              
     Amended and Restated Loan and Security Agreement, dated as of December 12,
     1997, between Foothill and Borrower.

                b.   The following definitions contained in Section 1.1 of
                                                            -----------   
the Agreement are amended and restated in their entirety to read as follows:

                "Applicable Margin" means: (a) prior to the Seventh Amendment
                 -----------------                                           
     Closing Date, one and three-quarters percent (1.75%) per annum; and (b) on
     and after the Seventh Amendment Closing Date, three percent (3.00%) per
     annum.

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<PAGE>
 
               "Permitted Overadvance Amount" means: (a) prior to March 1, 1997,
                ----------------------------                                    
     zero dollars; (b) during March, 1997, $1,000,000; (c) during April, 1997,
     $950,000; (d) during May, 1997, $900,000; (e) during June, 1997, $850,000;
     (f) during July, 1997, $800,000; (g) during August, 1997, $650,000; (h)
     during September, 1997, $300,000; (i) during October, 1997, $300,000; (j)
     during November, 1997, $300,000; (k) during the period commencing on
     December 1, 1997 and ending on January 30, 1998, $300,000; and (l) from and
     after January 31, 1998, zero dollars.

               "Loan Documents" means this Agreement, the First Amendment, the
                --------------                                                
     Second Amendment, the Third Amendment, the Fourth Amendment, the Sixth
     Amendment, the Seventh Amendment, the Suretyship Agreement, any Lock Box
     Agreement, any note or notes executed by Borrower and payable to Foothill,
     and any other agreement entered into by Borrower or any Affiliate of
     Borrower in connection with this Agreement.

               c.   The following specified provisions of the Agreement
hereby are amended and restated in their entirety as follows:

                    (1) Section 2.5(a)&(b)&(c):
                        ---------------------- 

               2.5  INTEREST:  RATES, PAYMENTS, AND CALCULATIONS.

                    (a) Interest Rate.  All Obligations, except for the Bridge
     Loan and undrawn L/Cs and L/C Guarantees, shall bear interest, on the
     average Daily Balance, at a rate equal to the Reference Rate plus the
     Applicable Margin. The Bridge Loan shall bear interest at the rate of 16.5%
     per annum.

                    (b) Default Rate.  All Obligations, except for the Bridge
     Loan, undrawn L/Cs and L/C Guarantees, shall bear interest, from and after
     the occurrence and during the continuance of an Event of Default, at a rate
     equal to the Reference Rate plus the Applicable Margin plus four (4.00)
     percentage points. From and after the occurrence and during the continuance
     of an Event of Default, the Bridge Loan shall bear interest at the rate of
     20.5% per annum. From and after the occurrence and during the continuance
     of an Event of Default, the fee provided in Section 2.2(d) shall be
                                                 --------------
     increased to a fee equal to that certain percentage per annum equal to the
     Applicable Margin plus four (4.00) percentage points times the average
     Daily Balance of the undrawn L/Cs and L/C Guarantees that were outstanding
     during the immediately preceding month.

                    (c) Minimum Interest.  In no event shall the rate of
     interest chargeable hereunder be less than ten percent (10.00%) per annum.

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                    (2) Section 2.9:
                        ----------- 

               2.9  BRIDGE LOAN.  Foothill: (a) agreed to make a bridge loan to
     Borrower on the closing date of the Third Amendment (the "Initial Bridge
     Loan"); and (b) has agreed to make an additional bridge loan to Borrower in
     the manner set forth below (the "Additional Bridge Loan"); in the original
     aggregate principal amount of $3,075,000 (the Initial Bridge Loan and the
     Additional Bridge Loan shall be referred to herein, collectively, as the
     "Bridge Loan").  The Additional Bridge Loan shall consist of, and be made
     in, three installments as follows: (i) $825,000 concurrently with the
     execution and delivery of the Seventh Amendment, of which the first $75,000
     shall be used solely to pay Foothill the "Additional Bridge Loan Fee" (as
     defined in Section 4.a of the Seventh Amendment); (ii) $750,000 on December
     15, 1997; and (iii) solely if and only if the Definitive Purchase Agreement
     Condition is fully and timely satisfied, $250,000 on January 1, 1998.  The
     principal of the Bridge Loan shall be repaid in monthly installments of
     principal in the following amounts:


 
 
                DUE DATE                       INSTALLMENT AMOUNT
 
              June 1, 1997                           $250,000  
 
              July 1, 1997                           $250,000
 
              August 1, 1997                         $250,000          
 
              September 1, 1997                      $    -0- 
 
              October 1, 1997                        $    -0-            
 
              November 1, 1997                       $    -0-
 
              December 1, 1997                       $    -0-
 
              January 1, 1998                        $    -0-
 
              January 31, 1998                       if the third installment of
                                                     the Additional Bridge Loan
                                                     is funded under clause
                                                     (b)(iii) above, $3,075,000;
                                                     otherwise, $2,825,000


     The outstanding principal balance and all accrued and unpaid interest under
     the Bridge Loan shall be due and payable upon the earlier to occur of: (y)
     January 31, 1998, and (z) the termination of this Agreement, whether by its
     terms, by prepayment, by acceleration, or otherwise.  The unpaid principal
     balance of the 

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<PAGE>
 
     Bridge Loan may be prepaid in whole or in part without penalty or premium
     at any time during the term of this Agreement upon 10 days prior written
     notice by Borrower to Foothill, all such prepaid amounts to be applied to
     the installments due on the Bridge Loan in the inverse order of their
     maturity. All amounts outstanding under the Bridge Loan shall constitute
     Obligations.

          d.   The following provisions hereby are added to the Agreement as a
new Section 6.20 thereof in proper alphanumerical order:

          6.20 DEFINITIVE PURCHASE AGREEMENT TIMETABLE.

               (a) On or before January 1, 1998, Borrower shall deliver to
     Foothill evidence satisfactory to Foothill that: (i) Borrower and
     Prospective Purchaser have entered into the Definitive Purchase Agreement;
     and (ii) the Definitive Purchase Agreement is in full force and effect.
     Borrower promptly shall deliver to Foothill copies of all material interim
     drafts of the Definitive Purchase Agreement and promptly provide to
     Foothill, upon reasonable request, such other materials or information
     relative to the Definitive Purchase Agreement and the transactions
     contemplated therein.

               (b) On or before January 31, 1998, Borrower shall deliver to
     Foothill evidence satisfactory to Foothill that Borrower has duly filed a
     Form S-4 registration statement, in respect of the Definitive Purchase
     Agreement and the transactions contemplated therein, with the Securities
     Exchange Commission ("SEC") in accordance with the rules and regulations of
     the SEC promulgated under the Securities Act of 1933, as amended.

               (c) On or before March 31, 1998, Borrower shall deliver to
     Foothill evidence satisfactory to Foothill that the Form S-4 registration
     statement in respect of the Definitive Purchase Agreement and the
     consummation of the transactions contemplated therein is effective.

               (d) On or before March 31, 1998, Borrower shall deliver to
     Foothill evidence satisfactory to Foothill that the audited financial
     statements of Borrower described in Section 6.4(b) of the Agreement in
     respect of Borrower's fiscal year ended December 31, 1997 shall have been
     duly issued in accordance with the rules and regulations of the SEC
     promulgated under the Securities Act of 1933, as amended.

               (e) On or before April 30, 1998, Borrower shall deliver to
     Foothill evidence satisfactory to Foothill that the requisite shareholders
     of Phoenix 

                                       6
<PAGE>
 
     have approved the Definitive Purchase Agreement and the consummation of the
     transactions contemplated therein.

                     (f) On or before May 31, 1998, Borrower shall deliver to
     Foothill evidence satisfactory to Foothill that the transactions
     contemplated in the Definitive Purchase Agreement shall have been
     consummated in accordance with the terms and conditions thereof and with
     all applicable law.

                e.   All references in the Agreement and each of the
other Loan Documents to any of the following terms or words of like import
therein referring to any of the following terms hereby are deleted from the
Agreement and such other Loan Documents: "the Fifth Amendment"; "the Sprint
Subordination Agreement"; and "TNC Sub".


          2.    Maturity Date of Bridge Loan and Permitted Overadvance
                ------------------------------------------------------
Amount; Supplemental Credit.  Borrower expressly and unmistakably acknowledges
---------------------------                                                   
and agrees that Foothill in its sole discretion may, but has no obligation or
commitment (express or implied) to: (a) extend the maturity date of the Bridge
Loan and the Permitted Overadvance Amount beyond January 31, 1998; or (b) extend
supplemental credit in the form of additional bridge loans or additional
permitted overadvance facilities.  Despite the fact that Borrower and Foothill
have been engaged in discussions and negotiations that Borrower hopes may lead
to such extensions, Foothill has not agreed to any extensions of either such
maturity date or such supplemental credit and, if Foothill elects not to extend
such maturity date, the Obligations of Borrower in respect of the Bridge Loan
and the Permitted Overadvance Amount will be due and payable on the date
provided for in the Agreement, as amended by this Amendment.  Borrower
recognizes that the agreements by Foothill to extend the maturity date of the
Bridge Loan and the Permitted Overadvance Amount from January 9, 1998 to January
31, 1998 and to provide the Additional Bridge Loan pursuant to the amendments to
the Agreement effected by this Amendment are being done solely as an
accommodation to Borrower to allow additional time beyond January 9, 1998 for
Borrower to negotiate and enter into the Definitive Purchase Agreement.
Borrower acknowledges and agrees that the decision, if any, by Foothill to
extend such maturity date or such supplemental credit may be subject to, without
limitation, the approval of and terms and conditions imposed by Foothill's
senior credit committee in its sole discretion and the progress or lack of
progress by Borrower in respect of the Definitive Purchase Agreement and the
transactions contemplated therein as determined by Foothill in its sole
discretion.


          3.    Representations and Warranties.  Borrower hereby
                ------------------------------                  
represents and warrants to Foothill that (a) the execution, delivery, and
performance of this Amendment and of the Agreement, as amended by this
Amendment, are within its corporate powers, have been duly authorized by all
necessary corporate action, and are not in contravention of any 

                                       7
<PAGE>
 
law, rule, or regulation, or any order, judgment, decree, writ, injunction, or
award of any arbitrator, court, or governmental authority, or of the terms of
its charter or bylaws, or of any contract or undertaking to which it is a party
or by which any of its properties may be bound or affected, and (b) this
Amendment and the Agreement, as amended by this Amendment, constitute Borrower's
legal, valid, and binding obligation, enforceable against Borrower in accordance
with its terms.


          4.    Conditions Precedent to Amendment.  The satisfaction of
                ---------------------------------                      
each of the following, on or before the Seventh Amendment Closing Deadline,
unless waived or deferred by Foothill in its sole discretion, shall constitute
conditions precedent to the effectiveness of this Amendment and each and every
provision hereof:

                a. Payment to Foothill by Borrower in immediately available
funds of a one-time funding fee in the amount of $75,000 in respect of the
Additional Bridge Loan (the "Additional Bridge Loan Fee"), which fee shall be
fully earned, non-refundable, due, and payable, upon the execution and delivery
of this Amendment by Foothill and Borrower, and which fee Borrower hereby
authorizes Foothill to charge to Borrower's loan account as part of the
Additional Bridge Loan;

                b. Payment to Foothill by Borrower in immediately available
funds of a one-time amendment fee in the amount of $50,000 in respect of the
closing of the Seventh Amendment, which fee shall be fully earned, non-
refundable, due, and payable, upon the execution and delivery of this Amendment
by Foothill and Borrower, and which fee Borrower hereby authorizes Foothill to
charge to Borrower's loan account as a revolving advance under Section 2.1 of
the Agreement;

                c. Foothill shall have received a certificate from the Secretary
of Phoenix attesting to the incumbency and signatures of authorized officers of
Phoenix and to the resolutions of Phoenix's Board of Directors ratifying its
prior execution and delivery of the Sixth Amendment and authorizing its
execution and delivery of this Amendment and the other Loan Documents to which
it is a party and contemplated in the Sixth Amendment and this Amendment and the
performance of the Sixth Amendment, this Amendment, the Agreement as amended by
the Sixth Amendment and this Amendment, and such other Loan Documents, and
authorizing specific officers of Phoenix to execute and deliver the same;

                d. Foothill shall have received a certificate from the Secretary
of PNAC attesting to the incumbency and signatures of authorized officers of
PNAC and to the resolutions of PNAC's board of directors or equivalent governing
body ratifying its prior execution and delivery of the Sixth Amendment and
authorizing its execution and delivery of this Amendment and the other Loan
Documents to which it is a party and contemplated in the Sixth Amendment and
this Amendment and the performance of the Sixth Amendment,

                                       8
<PAGE>
 
this Amendment, the Agreement as amended by the Sixth Amendment and this
Amendment, and such other Loan Documents, and authorizing specific officers of
PNAC to execute and deliver the same;

             e. Foothill shall have received a certificate from the Secretary of
AmeriConnect attesting to the incumbency and signatures of authorized officers
of AmeriConnect and to the resolutions of AmeriConnect's board of directors or
equivalent governing body ratifying its prior execution and delivery of the
Sixth Amendment and authorizing its execution and delivery of this Amendment and
the other Loan Documents to which it is a party and contemplated in the Sixth
Amendment and this Amendment and the performance of the Sixth Amendment, this
Amendment, the Agreement as amended by the Sixth Amendment and this Amendment,
and such other Loan Documents, and authorizing specific officers of AmeriConnect
to execute and deliver the same;

             f. Foothill shall have received an opinion of counsel to Borrower
in form and substance satisfactory to Foothill in its reasonable discretion;

             g. The representations and warranties in this Amendment, the
Agreement as amended by this Amendment, and the other Loan Documents shall be
true and correct in all respects on and as of the date hereof, as though made on
such date (except to the extent that such representations and warranties relate
solely to an earlier date);

             h. Except for any non-compliance by Borrower, with respect to the
fiscal quarter ending September 30, 1997, with one or more of the financial
covenants set forth in Section 6.14 of the Agreement, no Event of Default or
event which with the giving of notice or passage of time would constitute an
Event of Default shall have occurred and be continuing on the date hereof, nor
shall result from the consummation of the transactions contemplated herein;

             i. No injunction, writ, restraining order, or other order of any
nature prohibiting, directly or indirectly, the consummation of the transactions
contemplated herein shall have been issued and remain in force by any
governmental authority against Borrower or Foothill; and

             j. All other documents and legal matters in connection with the
transactions contemplated by this Amendment shall have been delivered or
executed or recorded and shall be in form and substance satisfactory to Foothill
and its counsel.


          5. Effect on Agreement. The Agreement, as amended hereby, shall be and
             -------------------
remain in full force and effect in accordance with its respective terms and
hereby is ratified and confirmed in all respects. Except as expressly set forth
herein, the execution, delivery,

                                       9
<PAGE>
 
and performance of this Amendment shall not operate as a waiver of, or as an
amendment of, any right, power, or remedy of Foothill under the Agreement, as in
effect prior to the date hereof. Borrower ratifies and reaffirms the continuing
effectiveness of the Suretyship Agreement with respect to the Agreement as
amended by this Amendment and the other Loan Documents.

          6. Further Assurances. Borrower shall execute and deliver all
agreements, documents, and instruments, in form and substance satisfactory to
Foothill, and take all actions as Foothill may reasonably request from time to
time, to perfect and maintain the perfection and priority of Foothill's security
interests in the Collateral, and to fully consummate the transactions
contemplated under this Amendment and the Agreement, as amended by this
Amendment.

          7. Miscellaneous.
             ------------- 

             a. Upon the effectiveness of this Amendment, each reference in the
Agreement to "this Agreement", "hereunder", "herein", "hereof" or words of like
import referring to the Agreement shall mean and refer to the Agreement as
amended by this Amendment.

             b. Upon the effectiveness of this Amendment, each reference in the
Loan Documents to the "Loan Agreement", "thereunder", "therein", "thereof" or
words of like import referring to the Agreement shall mean and refer to the
Agreement as amended by this Amendment.

             c. As used in this Amendment, "Seventh Amendment Closing Deadline"
means December 31, 1997.

             d. This Amendment shall be governed by and construed in accordance
with the laws of the State of California.

             e. This Amendment may be executed in any number of counterparts,
and/or by facsimile (followed promptly by delivery of original signatures), all
of which taken together shall constitute one and the same instrument and any of
the parties hereto may execute this Amendment by signing any such counterpart.

                                      10
<PAGE>
 
          IN WITNESS WHEREOF, the parties hereto have caused this Amendment to
be duly executed as of the date first written above.



                                   FOOTHILL CAPITAL CORPORATION,
                                   a California corporation


                                   By /s/ Kurt R. Marsden
                                      --------------------------

                                   Title: Vice President
                                          ----------------------



                                   PHOENIX NETWORK, INC., a Delaware corporation


                                   By /s/ Wallace M. Hammond
                                      --------------------------

                                   Title: President & CEO
                                          ----------------------



                                   PHOENIX NETWORK ACQUISITION CORP., a Delaware
                                   corporation


                                   By /s/ Wallace M. Hammond
                                      --------------------------

                                   Title: President & CEO
                                          ----------------------


                                   AMERICONNECT, INC., a Delaware corporation


                                   By /s/ Wallace M. Hammond
                                      --------------------------

                                   Title: President & CEO
                                          ----------------------

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