Part of the ABC transporter complex PhnCDE involved in phosphonates import. Responsible for energy coupling to the transport system. ATP + H2O + phosphonate(out) = ADP + H(+) + phosphate + phosphonate(in) The complex is composed of two ATP-binding proteins (PhnC), two transmembrane proteins (PhnE) and a solute-binding protein (PhnD). Belongs to the ABC transporter superfamily. Phosphonates importer (TC 3.A.1.9.1) family.