Abstract: Phase change material (PCM) filled porous bricks have garnered significant attention for enhancing building energy efficiency and indoor thermal comfort. However, the intrinsic mechanism by which the spatial layout of PCM within the porous brick regulates the thermal performance remains unclear, limiting the optimal design. To address this, the coupled effects of PCM spatial positions and contents (volume fraction) on thermal performances were investigated through numerical simulations of 8 distinct layout configurations by means of COMSOL Multiphysics. The results show that, the spatial layout, rather than mere the content, is the core variable determining the thermal regulation efficacy. Repositioning a single PCM layer from the exterior to the interior optimizes the spatiotemporal matching between the phase change process and the external temperature fluctuations. Through effective thermal attenuation and damping effects, this layout significantly reduces the inner surface temperature amplitude by 25.7% (from 12.69 ℃ to 9.43 ℃). Furthermore, this study quantifies the “law of diminishing marginal returns” associated with increasing PCM contents. Compared to the optimal single innerlayer layout (with a latent heat utilization rate of 0.97), double and triplelayer configurations exhibit reduced utilization rates of 0.82 and 0.83, respectively. This decline is attributed to insufficient thermal driving force acting on the inner PCM layers, resulting in material redundancy. In view of the tradeoff between thermal performance and material efficiency, the “single innerlayer layout” (Case D) is identified as the optimal solution, achieving significant performance gains with only 1/3 of the maximum PCM capacity. These findings propose a new design paradigm for dynamic energystorage envelopes, shifting from the conventional “thicker is better” approach to a “precise layout” strategy based on spatiotemporal synergy.