Thermal behavior of cement-based mortar, which is commonly used for plastering in buildings, can be significantly improved by integrating phase change materials (PCMs). PCMs are known for their ability to hold and release heat, making them excellent materials for improving the thermal performance of buildings. This study explores the thermal analysis of a building incorporated with PCM-based cement mortar wall panel using COMSOL Multiphysics® software. A PCM is prepared using vermiculite which is impregnated with capric acid (CA) and absolute ethanol (AE) which has proven significant thermal stability. The combination of PCM, coconut fiber, and nano silica incorporated in cement mortar sample demonstrated superior mechanical and thermal properties among the different cement mortar composites. The inclusion of these materials helps to manage hydration heat and improves thermal insulation, reducing the risk of thermal stress and cracking. The simulation findings indicate that these composites can significantly improve thermal comfort in buildings, offering a sustainable and energy-efficient solution compared to non-insulated building structures.