We report a P L_{2, 3} VV Auger line-shape study of the early stages of the GaP(110)/Yb interface formation. Strong similarities with the evolution displayed by the Si L_{2, 3} VV Auger profiles measured from the Si(111)/Yb interface and nearly-d⁰ metal silicides (Ca-silicides, Gd-silicides) is pointed out and exploited to determine the character of the P 3p-derived valence states in the Yb phosphide-like reaction products. A comparison, at different Yb coverages, with the self-folded partial density of states calculated for stoichiometric YbP is moreover performed. On this basis, the chemical bond is mainly described in terms of the formation of P 3p-Yb 5d hybrids.