A phase field method is used to computationally study conducting channel morphology of resistive switching thin film structures. Our approach successfully pre- dicts the formation of conducting channels in typical dielectric thin film structures, comparable to a range of resistive switches, o↵ering an alternative computational for- mulation based on metastable states treated at the atomic scale. In contrast to previous resistive switching thin film models, our formulation makes no a priori assumptions on conducting channel morphology and its fundamental transport mechanisms.