Phathom Pharmaceuticals Inc美股招股说明书(2026-01-07版)

PRELIMINARY PROSPECTUS SUPPLEMENT(to Prospectus dated January7, 2026) Common StockPre-Funded Warrants to Purchase Shares of Common Stock We are offeringshares of our common stock, $0.0001 par value per share, in this offering. We are also offering, in lieuof shares of common stock to certain investors that so choose, pre-funded warrants to purchase shares of our common stock. Thepurchase price of each pre-funded warrant equals the price per share at which the shares of our common stock are being sold inthis offering, minus $0.001, which is the exercise price of each pre-funded warrant per share. Each pre-funded warrant will be Our common stock is listed on the Nasdaq Global Select Market under the symbol “PHAT.” On January6, 2026, the lastreported sale price of our common stock on the Nasdaq Global Select Market was $16.37 per share. There is no establishedpublic trading market for the pre-funded warrants, and we do not expect a market to develop. We do not intend to list the Investing in our securities involves a high degree of risk. Please read “Risk Factors” beginning onpage S-5 of this prospectus supplement, on page 5 of the accompanying prospectus and thedocuments incorporated by reference into this prospectus supplement and the accompanying Neither the Securities and Exchange Commission nor any state of securities commission has approved or disapproved ofthese securities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Anyrepresentation to the contrary is a criminal offense. The information in this preliminary prospectus supplement and the accompanying prospectus is not complete and may be changed. A registration statement relating to thesecurities has been declared effective by the Securities and Exchange Commission. This preliminary prospectus supplement and the accompanying prospectus are not anoffer to sell these securities and are not soliciting offers to buy these securities in any jurisdiction where the offer or sale is not permitted.We have granted the underwriters an option for a period of 30 days to purchase an additionalshares of our commonstock. If the underwriters exercise the option in full, the total underwriting discounts and commissions payable by us will be Cantor Guggenheim Securities Table of Contents ABOUT THIS PROSPECTUS SUPPLEMENT This prospectus supplement and the accompanying prospectus dated January7, 2026 are part of a registration statement that we filed with the Securitiesand Exchange Commission, or SEC, as a “well-known seasoned issuer” as defined in Rule 405 under the Securities Act of 1933, as amended, or theSecurities Act, utilizing a “shelf” registration process. This prospectus supplement and the accompanying prospectus relate to the offer by us of shares ofour common stock and pre-funded warrants to certain investors. We provide information to you about this offering of shares of our common stock andpre-funded warrants in two separate documents that are bound together: (1)this prospectus supplement, which describes the specific details regardingthis offering; and (2)the accompanying prospectus, which provides general information, some of which may not apply to this offering. Generally, whenwe refer to this “prospectus,” we are referring to both documents combined. If information in this prospectus supplement is inconsistent with theaccompanying prospectus, you should rely on this prospectus supplement. However, if any statement in one of these documents is inconsistent with astatement in another document having a later date—for example, a document incorporated by reference in this prospectus supplement or the You should rely only on information contained in or incorporated by reference into this prospectus supplement and the accompanying prospectus andany free writing prospectus that we authorize. We and the underwriters have not, authorized anyone to provide you with information that is different. Weare offering to sell and seeking offers to buy shares of our common stock and pre-funded warrants only in jurisdictions where offers and sales arepermitted. The information contained in this prospectus supplement, the accompanying prospectus, the documents and information incorporated by In this prospectus supplement, unless the context otherwise indicates, the terms “Phathom,” the “Company,” “we,” “our” and “us” or similar terms referto Phathom Pharmaceuticals, Inc. Phathom, the Phathom logo, and other trademarks or service marks of Phathom appearing in this prospectus supplement are the property of Phathom.This prospectus supplement and the accompanying prospectus also includes trademarks, tradenames and service marks that are the property of otherorganizations. Use or display by us of other parties’ trademarks, trade dress or products is not intended to and does not imply a relationship with, orendorsements or sponsorship of, us by the trademark or trade dress owner. Solely for convenience, trademarks a