P4 +OH- --->PH3 + H2PO2-
Balance it medium is not specified .
Please don't attach any links and only by ion electron method .

Dear student,

Step 1: Write the two half-reactions as follows:
Oxidation half-reaction: P₄→ PH₃
 Reduction half-reaction: P₄ → H₂ PO₂^-
 Step:2
 Balance the atoms other than O and H
Oxidation half-reaction: P₄→  4PH₃
 Reduction half-reaction: P₄→  4H₂PO₂^-
Step:3
Balance the O and H atoms using H₂O and H⁺.
 Oxidation half-reaction: P₄ +12H⁺→  4PH³
Reduction half-reaction: P₄ +8H₂O→  4H₂ PO₂^- +8H⁺
Step:4
 Balance the charges using electrons
 Oxidation half reaction : P₄ +12H⁺ +12e→  4PH₃
Reduction half-reaction: P₄ +8H₂O→ 4H₂PO₂^- +8H⁺ +4e
 Step: 5
Multiply the reduction half reaction with 3 and add to the oxidation half reaction in order to get the net reaction after canceling the electrons.
 Oxidation half reaction : P4 +12H+ +12e→  4PH3
 Reduction half reaction: P4 +8H2 O→  4H2PO2- +8H+ +4e ] ×3
Net reaction:
4P₄+12H⁺+24H₂O→ 4PH₃+12H₂PO₂^-+24H⁺
Or
4P₄+24H₂O→ 4PH₃+12H₂PO₂^-+12H⁺
Step:6 As the reaction takes place in basic medium add 12OH ions on both sides in order to neutralize 12H .
 4 P₄ +24H₂O+12OH^-→ 4PH₃+12H₂PO₂^-+12H⁺ +12OH^-
Or
 4P₄ +24H₂O+12OH^-→ 4PH₃ +12H₂PO₂^- +12H₂O
Balanced chemical equation is:
 4P4 + 12OH^- + 12H₂O→ 4PH₃ + 12H₂PO₂^-
Regards