Phosphabenzamidine [mes-NH-C(Ph)═P-mes) (1) and phosphaformamidine (mes-NH-CH═P-mes) (4) ligands have been synthesized and characterized. The conjugate bases of 1 and 4 coordinate by each bridging three Cu(I) ions, forming hexa- and tetranuclear clusters Cu6[mes-N═C(Ph)-P-mes]3Cl4Li(THF)2 (3) and Cu4[mes-N═CH-P-mes]4 (5), respectively. Both clusters have been fully characterized using 1H NMR, 31P NMR, and X-ray crystallography. Complexes 3 and 5 exhibit a previously unknown coordination mode of phosphaamidinates, which are far less studied than their well-known amidinate counterparts.