Ammonium phosphoricum acts prominently on the nervous system, joints, and urinary organs. It is particularly useful in conditions of gout, arthritis, sciatica, and paralysis where there is stiffness, weakness, or sharp shooting pains. It also has a role in urinary disorders, especially where there is phosphatic urine (milky, cloudy deposits) with burning and weakness.

Another sphere of action is the nervous system, where it is indicated in paralysis, tremors, and weakness, often after exhausting diseases. It is also helpful in chronic catarrh of the throat and respiratory tract, with thick mucus and hoarseness.