4 Zn0 + H3PVO4 + 8 HCl P-IIIH3 + 4 ZnIICl2 + 4 H2O

This is an oxidation-reduction (redox) reaction:

PV + 8 e- P-III (reduction)

4 Zn0 - 8 e- 4 ZnII (oxidation)

H3PO4 is an oxidizing agent, Zn is a reducing agent.