Abstract: By simplifying catalyst–product separation and reducing phosphorus waste, heterogeneous hydroformylation offers a more sustainable alternative to homogeneous processes. However, heterogeneous hydroformylation catalysts developed thus far still suffer from the issues of much lower activity and metal leaching, which severely hinder their practical application. Here, we demonstrate that incorporating phosphorus (P) atoms into graphitic carbon nitride (PCN) supports facilitates charge transfer from Rh to the PCN support, thus largely enhancing electronic metal–support interactions (EMSIs). In the styrene hydroformylation reaction, the activity of Rh₁/PCN single-atom catalysts (SACs) with varying P contents exhibited a volcano-shaped relationship with P doping, where the Rh₁/PCN SAC with optimal P doping showed exceptional activity, approximately 5.8- and 3.3-fold greater than that of the Rh₁/g-C₃N₄ SAC without P doping and the industrial homogeneous catalyst HRh(CO)(PPh₃)₃, respectively. In addition, the optimal Rh₁/PCN SAC catalyst also demonstrated largely enhanced multicycle stability without any visible metal aggregation owing to the increased EMSIs, which sharply differed from the severe metal aggregation of large nanoparticles on the Rh₁/g-C₃N₄ SAC. Mechanistic studies revealed that the enhanced catalytic performance could be attributed to electron-deficient Rh species, which reduced CO adsorption while simultaneously promoting alkene adsorption through increased EMSIs. These findings suggest that tuning EMSIs is an effective way to achieve SACs with high activity and durability.