P40 + 4 NaOH + 2 H2O 2 Na2HPIIIO3 + 2 P-IIIH3

This is an oxidation-reduction (redox) reaction:

2 P0 + 6 e- 2 P-III (reduction)

2 P0 - 6 e- 2 PIII (oxidation)

Change the oxidation states