Regulating interfacial charge behavior in multiphase heterostructures is crucial for achieving high-performance electromagnetic wave (EMW) absorption, yet the synergistic optimization of dielectric loss and impedance matching remains a major challenge. Herein, a phosphorus (P) atom doping strategy is proposed to modulate the interfacial properties of a multiphase Co₂N/Co₃S₄/VN/VS heterostructure. P-doping reconstructs the heterointerfaces, promotes charge redistribution, and generates abundant polarization centers, thereby simultaneously optimizing charge transport and polarization relaxation. Density functional theory (DFT) calculations further reveal the vital role of interfacial charge redistribution in boosting polarization behavior. Consequently, the optimized P-CVNS heterostructure achieves a reflection loss (RL) of −36.93 dB and an effective absorption bandwidth (EAB) of 4.0 GHz at a matching thickness of 2.4 mm. This work reveals the pivotal role of heteroatom-doped interface engineering in optimizing EMW absorption and presents a scalable strategy for designing high-performance absorbers.