The Raman spectra of P4 and P2 mols. were studied in N, Ar, Kr, and Xe matrixes at 15 K. The vibrational frequencies of the P4 mol. are up to 14 cm-1 higher than the exptl. gas phase data. This apparent blue-shift is not caused by matrix effects but rather due to an underestimation of the fundamentals in the gas phase as a course of the elevated temps. The obsd. frequencies confirm a recent theor. prediction from high-level calcns. From the obsd. frequencies of the P4 mol. a general valence force field was calcd.