18 P + 32 H2O + 5 I2 → 10 PH4I + 8 H3PO4
This is an oxidation-reduction (redox) reaction:
10 P0 + 30 e- → 10 P-III (reduction)
8 P0 - 40 e- → 8 PV (oxidation)
10 I0 + 10 e- → 10 I-I (reduction)
P is an oxidizing agent, P is a reducing agent, I2 is an oxidizing agent.