Point defects in wide-bandgap semiconductors offer spin and photonic qubits in a solid-state platform, making them important building blocks for quantum information processing, communication, and sensing. While these systems have the strong advantage of room-temperature operation, intrinsic electron-phonon interaction induces broad phonon-sideband emission and weak zero-phonon-line transitions, limiting efficient spin-photon interfaces and scalable photon-mediated interaction. Here, we introduce a controlled heterophase interface based on the remote epitaxy technique as a crystal heterogeneity-engineering strategy. While stacking faults are treated as imperfections to be eliminated, our results instead show that crystal-phase interfaces can provide an additional degree of freedom to engineer defect-phonon interaction beyond the intrinsic properties of a single crystal. In comparison with single-phase 4H-silicon carbide (SiC) membranes, Vsi in 3C/4H heterointerface SiC exhibits a drastic enhancement of zero-phonon optical transitions, with a substantially narrower zero-phonon linewidth of 4.71 meV even at room temperature. These results establish heterophase-interface engineering as an effective route for tailoring defect-phonon interactions and realizing bright room-temperature quantum emitters with enhanced zero-phonon optical transitions.