Iron redox cycling governs the early diagenesis of organic matter (OM) and significantly influences phosphorus (P) dynamics in aquatic systems. The release of endogenous P during freezing periods carries significant ecological implications for these systems. However, it remains unclear whether microbial dissimilatory iron reduction maintains a dominant role under anoxic freezing conditions, and the potential impact of weakened microbial-mediated P release via this pathway has not been adequately addressed. This study established an overlying water-porewater-sediment core microcosm system based on the ecological principle of stratified microbial communities along natural redox gradients to investigate the regulatory mechanisms of iron-dissimilatory reduction processes driven by distinct microbial species on endogenous P release during the freeze period. The results demonstrated higher P concentrations in overlying water for microbial treatment groups than controls, particularly during early stages with high microbial activity. Enhanced microbial metabolism intensified iron oxide reduction and organic P (OP) degradation. A significant correlation between inorganic P (IP) and Fe2+in the water-porewater-sediment system indicated that the interfacial processes of sediments substantially influence overlying water chemistry via the bridging effect of porewater, highlighting endogenous pollution on water quality. It was observed that nitrate-reducing bacteria preferentially degraded OM and OP to release P, while dissimilatory iron-reducing bacteria primarily reduced dissolved iron oxides, liberating iron-bound P. These findings reveal distinct P release mechanisms and sources under varying microbial activity and environmental conditions. Furthermore, the sediment's iron reduction zone (8-10 cm) was identified as a hotspot layer for P release, offering critical insights for optimal dredging depth in lake management. This study emphasizes the role of microbial activity in the endogenous P release during freezing periods, particularly OP release, which may serve as an initial nutrient supply for algal blooms in spring and summer. These findings advance understanding of the role of iron oxides in seasonal redox boundary shifts and P dynamics in lake sediments within cold and arid regions.