Phathom Pharmaceuticals Reports Third Quarter 2023 Results and Recent Business Updates VOQUEZNA (vonoprazan) tablets approved by the U.S. Food and Drug Administration (FDA) for the treatment of Erosive GERD and relief of

Phathom Pharmaceuticals Reports Third Quarter 2023 Results and Recent Business Updates

November 9, 2023 Phathom Pharmaceuticals, Inc. (Nasdaq: PHAT), a biopharmaceutical company focused on developing and commercializing novel treatments for gastrointestinal diseases, today reported financial results for

the third quarter of 2023 and provided updates on recent regulatory and business progress.

Our recent FDA approval of VOQUEZNA makes 2023 another

significant year for Phathom and marks a pivotal moment in our journey to bring a new class of treatment options to millions of patients in the U.S. with acid related disorders, said Terrie Curran, President and Chief Executive Officer of

Phathom. We are completing the buildout and onboarding of our sales team to execute our highly anticipated launch and have already begun branded promotion in advance of VOQUEZNA s expected commercial availability in December. Our

organization also continues to make important regulatory progress to maximize the full commercial potential of vonoprazan, evidenced by our September NDA submission seeking approval of vonoprazan as a daily treatment for Non-Erosive GERD, the largest subcategory of GERD. With an additional $175 million in cash provided under our non-dilutive revenue interest financing agreement this

quarter, we believe we are well capitalized to support the blockbuster potential of VOQUEZNA.

Recent Clinical, Regulatory, and Business Updates:

Third Quarter 2023 Financial Results:

About Phathom Pharmaceuticals

Phathom Pharmaceuticals is a biopharmaceutical company focused on the development and commercialization of novel treatments for gastrointestinal

diseases. Phathom has in-licensed the exclusive rights in the United States, Europe, and Canada to vonoprazan, a first-in-class

potassium-competitive acid blocker (PCAB). For more information about Phathom, visit the Company s website at www.phathompharma.com and follow the Company on LinkedIn and Twitter.

Forward-Looking Statements

contains forward-looking statements. Investors are cautioned not to place undue reliance on these forward-looking statements, including statements about the timing of a U.S. commercial launch for vonoprazan for Erosive GERD, the timing of regulatory

review and commercial launch of vonoprazan as a daily treatment for Non-Erosive GERD, the timing of commencement of our Phase 3 Non-Erosive GERD trial, and our cash

runway. The inclusion of forward-looking statements should not be regarded as a representation by Phathom that any of its plans will be achieved. Actual results may differ from those set forth in this press release due to the risks and uncertainties

inherent in Phathom s business, including, without limitation: we may not be able to successfully commercialize VOQUEZNA which will depend on a number of factors including coverage and reimbursement levels from governmental authorities and

health insurers as well as market acceptance by healthcare providers; future data generated from our stability program may be different from the data submitted to the FDA to date and may not demonstrate that our mitigation efforts will continue to

maintain the level of the nitrosamine impurity below the acceptable intake (AI) level throughout the shelf life of products containing vonoprazan, which could result in market action or shelf life reduction; risks associated with product

manufacturing or formulation changes required to be made in connection with achieving the AI; the inherent risks of clinical development of vonoprazan; Phathom s dependence on third parties in connection with product manufacturing, research and

preclinical and clinical testing; regulatory developments in the United States and foreign countries; unexpected adverse side effects or inadequate efficacy of vonoprazan that may limit its development, regulatory approval and/or commercialization,

or may result in recalls or product liability claims; Phathom s ability to access additional capital under its term loan facility and royalty interest finance agreements is subject to certain conditions; Phathom s ability to obtain and

maintain intellectual property protection for vonoprazan; Phathom s ability to comply with its license agreement with Takeda; and other risks described in the Company s prior press releases and the Company s filings with the

Securities and Exchange Commission (SEC), including under the heading Risk Factors in the Company s Annual Report on Form 10-K and any subsequent filings with the SEC. You are cautioned not to

place undue reliance on these forward-looking statements, which speak only as of the date hereof, and Phathom undertakes no obligation to update such statements to reflect events that occur or circumstances that exist after the date hereof. All

forward-looking statements are qualified in their entirety by this cautionary statement, which is made under the safe harbor provisions of the Private Securities Litigation Reform Act of 1995.

VOQUEZNA, VOQUEZNA TRIPLE PAK, VOQUEZNA DUAL PAK, Phathom Pharmaceuticals, and their respective logos are

registered trademarks or trademarks of Phathom Pharmaceuticals, Inc.

Selected Condensed Balance Sheets

Statements of Operations and Comprehensive Loss

thousands, except share and per share amounts)