In a study of the v-P2O5 glassy structure, we discuss the complementarity of experimental and combined vibrational spectroscopies, namely infrared and polarized Raman scattering, using vibrational multipolar decomposition (VMD) analysis and ab initio calculations of local structures and vibrational spectra. VMD is a rigorous method that relates multiple vibrational spectroscopic activities of an isotropic medium to the point group symmetry of its elementary structural units (ESU) [see G. Guimbretiere et al., J. Phys. Chem. C 112 (2008) 17906]. These ESUs are molecule-like and can be efficiently modeled using ab initio cluster calculations. Information obtained by both analytical techniques is compared and discussed. Finally a detailed spectroscopic assignment is proposed.