Transition metal phosphides is a class of compounds which continuously attracts expanding interest in materials science. Raman spectroscopy is one of the basic methods in materials characterization, but it still has rudimentary implications in the analysis of phosphide-based materials. Meanwhile, high spatial resolution and tolerance to the surface quality might place this method in line with the electron microprobe analysis, allowing confident determination of both crystal structure and chemical composition of transition metal phosphides. We herein show the potential applications of Raman spectroscopy for the quantitative analysis of phosphide solid solutions, exemplified by the compounds related to the important join FeP–NiP.