3 P40 + 8 NaOH + 8 H2O 4 P-IIH2 + 8 NaH2PIO2

This is an oxidation-reduction (redox) reaction:

8 P0 - 8 e- 8 PI (oxidation)

4 P0 + 8 e- 4 P-II (reduction)

Change the oxidation states