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.