Laser-excited remote phosphor (LERP) systems are the next step in solid-state lighting technology. However, the thermal stability of phosphors has long been a major concern in the reliable operation of these systems. As a result, a simulation strategy is presented here that couples the optical and thermal effects, while the phosphor properties are modeled to temperature. A simulation framework is developed in which the optical and thermal models are defined in Python using appropriate interfaces to commercial software: the ray tracing software Zemax OpticStudio for the optical analysis and the finite element method (FEM) software ANSYS Mechanical for the thermal analysis. Specifically, the steady-state opto-thermal analysis model is introduced and experimentally validated in this study based on Ce:YAG single-crystals with polished and ground surfaces. The reported experimental and simulated peak temperatures are in good agreement for both the polished/ground phosphors in the transmissive and reflective setups. A simulation study is included to demonstrate the simulation’s capabilities for optimizing LERP systems.