Controllable covalent surface functionalization of black phosphorus (BP) remains a central challenge in the development of 2D phosphorus-based materials. Here, we report a scalable route to synthesize biodegradable BP-polymer hybrids and establish optimal conditions for BP production, exfoliation, and covalent modification. BP sheets, produced via optimized mechanochemical and exfoliation processes, are covalently functionalized with 2-azido-4,6-dichloro-1,3,5-triazine via a nitrene-mediated [2+1] cycloaddition. The reaction yields a P-N bond, verified by advanced surface analyses and density functional theory (DFT) calculations. The conjugated triazine groups enable subsequent nucleophilic aromatic substitution reactions, providing a versatile platform for controlled post-modification of BP surface. This covalent functionalization strategy addresses key limitations in BP surface chemistry and provides a route toward biodegradable phosphorus-based hybrid materials. As a representative example, functionalization with linear polyglycerol sulfate produces BP-polymer conjugates that inhibit respiratory syncytial virus (RSV) and herpes simplex virus 1 (HSV-1) at low-microgram-per-milliliter concentrations.