<p>Interfaces are commonly present in engineering materials and often serve as mechanically weak regions where cracks are prone to initiation. These cracks typically nucleate at the interface and subsequently propagate into the surrounding bulk material. The heterogeneity between the interface and the matrix complicates the simulation of their coupled fracture behavior. The treatment of material properties across the discontinuous interface critically influences the interplay between bulk fracture and interfacial debonding. An accurate prediction of crack paths across such heterogeneous interfaces remains a persistent challenge in computational mechanics. Within a unified variational framework, this study proposes an accurate phase-field model to capture complex failures in composites. Cracks and interfaces are both regularized via continuous phase-field variables, thereby eliminating geometric discontinuities and facilitating numerical implementation. An explicit analytical expression is derived to smoothly interpolate the critical energy release rate and material strength across interfaces, which ensures correct representation of interface toughness in the diffused regions. The model accommodates several generic softening laws and accurately characterizes the competition between crack deflection and penetration at interfaces. Numerical results demonstrate conservative mechanical responses, which are beneficial for safety–critical applications. This unified framework offers an accurate and efficient tool for simulating complex fracture behavior in composite and layered materials.</p>