Phosphorus is a mineral found in many foods. It works with calcium and vitamin D in your body to keep your bones healthy and strong. Healthy kidneys keep the right amount of phosphorus in your body, but when your kidneys are not working well, phosphorus can build up to dangerous levels in your blood. Many people with kidney disease need to limit the amount of phosphorus they eat. Depending on your stage of kidney disease, your doctor may also prescribe a medicine called a phosphate binder. Phosphate binders help to keep phosphorus from building up in your blood. Although phosphate binders help control the amount of phosphorus in your body, you will still need to watch how much phosphorus you eat.