8 LiMnO4 (aq) + 5 PH3 (g) + 12 H2SO4 (aq) → 4 Li2SO4 (aq) + 8 MnSO4 (aq) + 5 H3PO4 (aq) + 12 H2O (l)
This is an oxidation-reduction (redox) reaction:
5 P-III - 40 e- → 5 PV (oxidation)
8 MnVII + 40 e- → 8 MnII (reduction)
PH3 is a reducing agent, LiMnO4 is an oxidizing agent.