6 KMnO4 + 15 NaNO2 + 6 H3PO4 → 2 Mn3(PO4)2 + 15 NaNO3 + 2 K3PO4 + 9 H2O
This is an oxidation-reduction (redox) reaction:
6 MnVII + 30 e- → 6 MnII (reduction)
15 NIII - 30 e- → 15 NV (oxidation)
KMnO4 is an oxidizing agent, NaNO2 is a reducing agent.