Ammonium phosphate is the inorganic compound with the formula (NH<sub>4</sub>)<sub>3</sub>PO<sub>4</sub>. It is the ammonium salt of orthophosphoric acid. A related double salt, (NH<sub>4</sub>)<sub>3</sub>PO<sub>4</sub><sup>.</sup>(NH<sub>4</sub>)<sub>2</sub>HPO<sub>4</sub> is also recognized but is impractical to use. Both triammonium salts evolve ammonia. In contrast to the unstable nature of the triammonium salts, the diammonium phosphate (NH<sub>4</sub>)<sub>2</sub>HPO<sub>4</sub> and monoammonium salt (NH<sub>4</sub>)H<sub>2</sub>PO<sub>4</sub> are stable materials that are commonly used as fertilizers to provide plants with fixed nitrogen and phosphorus.
Ammonium phosphate is the main ingredient in pink fire retardant.
Triammonium phosphate can be prepared in the laboratory by treating 85% phosphoric acid with 30% ammonia solution:
(NH<sub>4</sub>)<sub>3</sub>PO<sub>4</sub> is a colorless, crystalline solid. The solid, which has the odor of ammonia, is readily soluble in water. The salt converts to diammonium hydrogen phosphate (NH<sub>4</sub>)<sub>2</sub>HPO<sub>4</sub>.