Ammonium phosphate is the salt of ammonium and phosphate. It is a highly unstable compound with the formula (NH4)3PO4.
In addition to (NH4)3PO4, a related double salt (NH4)3PO4.
(NH4)2HPO4 is also recognized. It too is unstable.
The instability of these salts results in their decomposition with release of ammonia.
(NH4)3PO4 → H(NH4)2PO4 + NH3
(NH4)3PO4 → H(NH4)2PO4 + NH3