The bonding situation within the P4O6Sm (m = 0-4) series is studied using a combination of experimental and theoretical vibrational analysis. A correlation between the spectra of the compounds is undertaken and the shifts of the vibrational frequencies within the series are analyzed. The frequency shifts found within the P4O6Sm (m = 0-4) series are furthermore compared with those found within the P4On (n = 6-10) series. Our analysis indicates a somewhat larger increases in the P-O cage bond strength in the oxygen-substituted compounds relative to the sulfur substitution. This interpretation is consistent with the same conclusion based on a comparison of the P-O bond lengths shortening in the cage in going from P4O6 to P4O10 (0.05 Angstrom) and P4O6 to P4O6S4 (0.03 Angstrom).