The design of van der Waals heterojunctions for modulating excitonic photoluminescence (PL) in two-dimensional (2D) semiconductors has become a major research focus in low-dimensional photonics. While previous studies have predominantly explored charge- and energy-transfer processes in transition metal dichalcogenides with emission wavelengths mostly in the visible range, there remains an urgent need to develop new heterojunction material platforms that extend emission into the near-infrared (NIR) telecommunication band for silicon-based on-chip light sources. Trilayer black phosphorus (3L BP) exhibits exciton-dominated NIR emission within the telecommunication window; however, its intrinsic emission intensity at room temperature is limited, constraining practical applications. Type-I band-aligned heterojunctions, which confine carriers within the narrow-bandgap emitting layer, provide an effective strategy to enhance radiative recombination and light emission in these materials. In this work, we fabricated a type-I van der Waals heterostructure composed of direct-bandgap 3L BP and indirect-bandgap bilayer tungsten diselenide (2L WSe₂). Compared with the isolated 3L BP and 2L WSe₂ regions, the heterostructure exhibits significantly enhanced NIR emission and suppressed visible emission at room temperature. Notably, unlike isolated BP, the heterostructure exhibits anomalous temperature-dependent PL behavior, with emission intensity increasing as the temperature rises. This suggests that enhanced lattice vibrations at higher temperatures promote thermal activation and carrier transfer from WSe₂ to BP, while simultaneously reducing the capture efficiency of nonradiative recombination centers. Furthermore, the gate-voltage-dependent PL of the 3L BP/2L WSe₂ heterostructure differs from that of isolated 3L BP. Under positive gate bias, the charge imbalance in p-type 2L WSe₂ is alleviated, which boosts carrier injection from WSe₂ to BP and enables tunability and enhanced radiative recombination. These findings demonstrate enhanced NIR excitonic emission in the type-I BP/WSe₂ heterostructure and provide a promising strategy for designing tunable, efficient, room-temperature light-emitting devices operating in the NIR telecommunication band.