Probably part of the ABC transporter complex PhnC2D2E2. Binds strongly to methylphosphonate (MPn), ethylphosphonate (EPn) and inorganic phosphite. The complex may be composed of two ATP-binding proteins (PhnC2), two transmembrane proteins (PhnE2) and a solute-binding protein (PhnD2). Belongs to the phosphate/phosphite/phosphonate binding protein family.