**Study Overview:** This clinical trial is testing a new treatment called **AP301** for people with high blood phosphate levels who are on dialysis. Dialysis is a treatment for kidney problems where a machine helps clean the blood. High phosphate levels can make people sick. The trial will see if **AP301** can lower these levels and improve people's lives, especially in China. Participants will stop current phosphate-lowering drugs and take **AP301** or a look-alike pill for a total of 35 weeks. The dose may change based on blood test results. **Key Points:** - **Duration:** The study lasts 35 weeks, with regular blood tests to check phosphate levels. - **Participation:** Must be 12 or older, on dialysis for at least 3 months, and have specific phosphate levels. - **Exclusions:** Cannot join if planning a kidney transplant, have certain medical conditions, or severe allergies. Participants might receive extra treatment if blood phosphate levels are too high or low. The study will monitor any side effects to ensure safety.