Phase change materials (PCMs) have gained significant attention as electrical/photonic materials due to their fast transition between two distinct phases. In this study, we propose a thermodynamically consistent coupled phase-field (PF) model that incorporates various physical phenomena, including phase transition (PT), heat transfer, thermoelectricity, and mechanics. This model provides a comprehensive understanding of temperature, stress, and phase evolution in amorphous GST PCRAM cells. The model predicts that the crystallization heat induces self-heating within the cell, and the nuclei continue to grow even after the voltage is removed—highlighting the crucial role in the thermal design of PCRAMs. Additionally, mechanical stresses can either accelerate or decelerate the phase transition, impacting the morphology of the crystallized cell.