H3PIIIO3 + 3 Zn0 + 6 HCl P-IIIH3 + 3 ZnIICl2 + 3 H2O

This is an oxidation-reduction (redox) reaction:

PIII + 6 e- P-III (reduction)

3 Zn0 - 6 e- 3 ZnII (oxidation)

H3PO3 is an oxidizing agent, Zn is a reducing agent.