The structural and spectroscopic properties of Na2O-Al2O3-SiO2-xP2O5 glasses (x=0 to 7 mol%) are investigated. Both Raman and IR spectra reveal that discrete phosphate species ([PO4]^{-3}, [PO3O_{1/2}]^{-2}) with low polymerization degree can be formed in the silicate glass. These phosphate structures scavenge non-bridging oxygen ions and cations from the silicate network, resulting in an increase of the glass transition temperature. According to the Judd-Ofelt intensity parameters (\Omega2;\Omega4;\Omega6) of Er3 , the asymmetry of local environment around Er3 becomes higher, and the bond covalency between Er3 and O^{2-} decreases after P2O5 is introduced. In the emission spectra, photoluminescence intensity increases with increasing P2O5 concentration and the spectra are inhomogeneously broadened, revealing that the ligand electric field around Er3 is dramatically changed, and the glass matrix becomes disordered.