Company: PHAT
Filing Date: 2025-03-06
Form Type: S-8
Source: 0001193125-25-048546
Chunk: 0

Company: Phathom Pharmaceuticals, Inc.
Filing Date: 2025-03-06
Form: S-8
Chunk 0
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As filed with the Securities and Exchange Commission on March 6, 2025 Registration No. 333- UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM S-8 REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933 PHATHOM PHARMACEUTICALS, INC. (Exact name of registrant as specified in its charter)

| Delaware                        |     | 82-4151574         |
| (State or Other Jurisdiction of 
 Incorporation or Organization)  |     | -I.R.S. Employer   
 Identification No. |

100 Campus Drive, Suite 102 Florham Park, New Jersey 07932 (877) 742-8466 (Address of Principal Executive Offices) PHATHOM PHARMACEUTICALS, INC. 2019 INCENTIVE AWARD PLAN PHATHOM PHARMACEUTICALS, INC. 2019 EMPLOYEE STOCK PURCHASE PLAN (Full Title of the Plans) Terrie Curran President and Chief Executive Officer Phathom Pharmaceuticals, Inc. 100 Campus Drive, Suite 102 Florham Park, New Jersey 07932 (877) 742-8466 (Name, Address and Telephone Number, Including Area Code, of Agent for Service) Copy to: Cheston J. Larson Matthew T. Bush Anthony A. Gostanian Latham & Watkins LLP 12670 High Bluff Drive San Diego, California 92130 (858) 523-5400 Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-acceleratedfiler or a smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b-2of the Exchange Act.

| Large accelerated filer |     | ☐ |     | Accelerated filer         |     | ☐ |
| Non-accelerated filer   |     | ☒ |     | Smaller reporting company |     | ☒ |
|                         |     |   |     | Emerging growth company   |     | ☐ |

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐ Proposed sales