Company: PHAT
Filing Date: 2025-03-06
Form Type: S-8
Source: 0001193125-25-048546
Chunk: 1

Company: Phathom Pharmaceuticals, Inc.
Filing Date: 2025-03-06
Form: S-8
Chunk 1
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 to take place as soon after the effective date of the registration statement as awards granted under the above-named plans are granted, exercised and/or distributed.

EXPLANATORY NOTE This registration statement registers the offer and sale of an additional 9,000,000 shares of common stock of Phathom Pharmaceuticals, Inc. for issuance under the 2019 Incentive Award Plan (the “2019 Plan”) and an additional 3,000,000 shares of common stock of Phathom Pharmaceuticals, Inc. for issuance under the 2019 Employee Stock Purchase Plan (the “ESPP”). In accordance with Instruction E to Form S-8,the contents of the prior registration statements on Form S-8,File No. 333-234357and File No. 333-263420, filed with the Securities and Exchange Commission (“SEC”) on October 28, 2019 and March 10, 2022, respectively, previously filed with respect to the 2019 Plan and the ESPP, are hereby incorporated by reference. PART I INFORMATION REQUIRED IN THE SECTION 10(a) PROSPECTUS The documents containing the information specified in Part I of Form S-8will be sent or given to participants as specified by Rule 428(b)(1) of the Securities Act. These documents and the documents incorporated by reference into this registration statement pursuant to Item 3 of Part II of this registration statement, taken together, constitute a prospectus that meets the requirements of Section 10(a) of the Securities Act. PART II INFORMATION REQUIRED IN THE REGISTRATION STATEMENT In this registration statement, Phathom Pharmaceuticals, Inc. is sometimes referred to as “Registrant,” “we,” “us” or “our.” Item 3. Incorporation of Documents by Reference. The SEC allows us to “incorporate by reference” the information we file with them, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is considered to be part of this registration statement, and later information filed with the SEC will update and supersede this information. We hereby incorporate by reference into this registration statement the following documents previously filed with the SEC:

| (b) | the description of the Registrant’s common stock set forth in the Registrant’s registration statement                                                                                                                             
 on Form 8-A12B/A (Registration No. 001-39094), filed by the                                                                                                                                                                       
 Registrant with the SEC under Section 12(b) of the Securities Exchange Act of 1934