In the title mol-ecule, C(17)H(20)NO(3)P, the P atom is bonded in a distorted tetra-hedral environment. The dihedral angle between the two phenyl rings is 23.52 (10)°. The phosphoryl and N-H groups are anti with respect to one another. The -CH(2)-CH(2)-CH(2)-CH(2)- sequence of atoms in the cyclo-pentyl ring is disordered over two sets of sites with refined occupancies of 0.574 (10) and 0.426 (10). In the crystal, mol-ecules are linked via N-H⋯O=P hydrogen bonds to form extended chains along [010].