The assignment of high-field (18.8 T) O-17 MAS and 3QMAS spectra has been completed by use of first-principles calculations for three crystalline sodium phosphates, Na3P3O9, Na5P3O10, and Na4P2O7. In Na3P3O9, the calculated parameters, cluadrupolar constant (C-Q), quadrupolar asymmetry (eta(Q)), and the isotropic chemical shift (delta(cs)) correspond to those deduced experimentally, and the calculation is mandatory to achieve a complete assignment. For the sodium tripolyphosphate Na5P3O10, the situation is more complex because of the free rotation of the end-chain phosphate groups. The assignment obtained with ab initio calculations can however be confirmed by the O-17{P-31) MAS-J-HMOC spectrum. Na4P2O7 O-17 MAS and 3QMAS spectra show a complex pattern in agreement with the computed NMR parameters, which indicate that all of the oxygens exhibit very similar values. These results are related to structural data to better understand the influence of the oxygen environment on the NMR parameters. The findings are used to interpret those results observed on a binary sodium phosphate glass.