Precise control over multiple functional phases in strongly correlated VO₂ and its heterostructures establishes a correlation between inclusions, defect dynamics and the stabilization of monoclinic versus tetragonal phases. However, a comprehensive atomic-level understanding of these processes remains insufficient to elucidate the underlying multiple defect-phase relationship mechanisms. Herein, we uncover the atomic-scale inter-layer defect transfer mechanism in VO₂-based Fabry-Pérot resonant cavity heterostructures under vacuum-ultraviolet (VUV) irradiation. The irradiation induces cleavage of In-O and Sn-O bonds within the indium-tin-oxide (ITO) layer, triggering the concerted diffusive migration of In, Sn, and oxygen vacancies with VO₂. This migration elevates electron occupancy in the hybridized energy levels of the d_//-bond orbital and In/Sn-d orbitals within V-V dimers. The enhanced d// electron density strengthens orbital overlap with π* antibonding orbitals, driving the VO₂ phase transition from insulating monoclinic to metallic rutile. These results offer important theoretical and experimental insights into defect-mediated phase engineering in strongly correlated oxides and hold promise for advancing applications in quantum optoelectronic information and adaptive optics.