Exhibit 99.1 Phathom Pharmaceuticals Reports Fourth Quarter and Full Year 2023 Financial Results and Provides Business Update • Launched VOQUEZNA® (vonoprazan) tablets in November 2023 for the treatment of Erosive GERD (gastroesophageal reflux disease), achieving net revenues of $0.7 million for the fourth quarter • Early physician prescribing demonstrates strong demand for VOQUEZNA • Secured expanded commercial coverage for VOQUEZNA with a top U.S. pharmacy benefit manager (PBM), growing commercial access ...