ADVERSE REACTIONS Gastrointestinal upset (diarrhea, nausea, stomach pain, and vomiting) may occur with the use of potassium phosphate. Also, bone and joint pain (possible phosphate-induced osteomalacia) could occur. The following adverse effects may be observed with potassium administration: irregular heartbeat; dizziness; mental confusion; weakness or heaviness of legs; unusual tiredness; muscle cramps; numbness, tingling, pain, or weakness in hands or feet; numbness or tingling around lips; shortness of breath or troubled breathing.