Metal-rich phases of general formula M2P have demonstrated interesting catalytic activity, e.g., for hydrogen evolution reaction and for hydrogenations in colloidal suspension. The production of well-crystallized nanoparticles of the M2P phase from commercial precursors on a large enough scale is not trivial as the existing routes generally require fairly high reaction temperatures and a large excess of the phosphorus source. Here, we selected a commercial aminophosphine, P(NEt2)3, as the phosphorus precursor (3 equiv or less) to develop a robust synthesis from CoCl2 (respectively NiCl2) that provided crystalline Co2P (respectively Ni2P) nanoparticles with high yields on a 9 mmol scale. Moreover, modification of the M2P nanoparticles via the addition of a molecular Lewis base is a promising route to trigger catalytic activity of the colloidal suspension at a lower temperature. For the hydrogenation of phenylacetylene catalyzed by Co2P and Ni2P nanoparticles, we showed that catalytic amounts of adequate phosphines, such as PnBu3 and also, in some instances, oleylamine, triggered a full conversion at lower temperatures than with the nanoparticles alone. We delineated the most efficient phosphines in the case of a Ni2P catalyst, using a stereoelectronic map of 13 phosphines.