The strategic design of photocatalysts with robust oxidative ability is essential for the efficient and sustainable elimination of volatile organic compounds (VOCs). Herein, we developed a phosphorus-doped ZnSn(OH)₆ photocatalyst (ZHS-P50) with self-modulated defects via a one-step microwave hydrothermal method. The optimized ZHS-P50 exhibits impressive photocatalytic performance, achieving a toluene (C₇H₈) removal efficiency of 95%. Notably, phosphorus (P) incorporation modulates oxygen vacancy (OV) concentrations via self-defect regulation, creating a synergistic interplay that enhances molecular activation. This synergy promotes O₂ adsorption and activation, leading to abundant generation of reactive oxygen species critical for photocatalysis. In situ spectroscopic analysis combined with theoretical calculations reveals that P doping and OVs facilitate the formation of benzoic acid as a key intermediate, accelerating ring-opening reactions and enabling deep mineralization. This work highlights ZHS-P50 as an efficient photocatalyst for C₇H₈ abatement and establishes a defect-regulation paradigm for advanced oxidation catalysts.