P4+3NaOH+3H2O→PH3+3NaH2PO2
In reactant P is present in (0) oxidation state and in PH3, it is present in (−3) oxidation state and in NaH2PO2 it is present in (+1) oxidation state. P undergoes both oxidation and reduction. So this is an example of disproportionation reaction.