The title room-temperature phase of (NH(4))(2)(PO(3)F) is orthorhombic (Pna2(1)) and is related to the beta-K(2)SO(4) structure family. The title structure consists of ammonium cations, NH(4)(+), and fluorophosphate anions, (PO(3)F)(2-). These ions are connected by N-H.O hydrogen bonds. Two-centre N-H.F hydrogen bonds are not present in the structure. Phase transitions were detected at 251+/-2 and 274+/-2 K during cooling and heating, respectively.