8 P0 + 9 NaOH + 3 H2O 3 Na3PVO4 + 5 P-IIIH3

This is an oxidation-reduction (redox) reaction:

5 P0 + 15 e- 5 P-III (reduction)

3 P0 - 15 e- 3 PV (oxidation)

Change the oxidation states