The rapid accumulation of bioavailable phosphorus (Bio-P) promotes ecosystem development at the beginning of pedogenesis in the Hailuogou Glacier foreland. However, the role of microorganisms in Bio-P accumulation during early pedogenesis remains unclear. Using the Hailuogou Glacier foreland on Gongga Mountain as a natural laboratory, microbial community assembly, co-occurrence networks, and phosphorus cycling genes (PCGs) were examined across four successional stages, from bare land to moss crust. The results showed that bacteria were dominant at all stages. Microbial diversity and evenness increased gradually, whereas the topological properties of the microbial network initially increased and then decreased. Community assembly is mainly driven by deterministic processes under environmental pressures. At the beginning of pedogenesis, microorganisms adapt to scarce Bio-P conditions by enhancing the functional potential of key PCGs (e.g., pqqE, gcd, phoD, and 3-Phytase), which mediate mineral phosphorus solubilization and organic phosphorus mineralization. Tight cooperative network structures within microbial communities and dominant microbial taxa were the major factors accelerating Bio-P. Thus, it can be concluded that microorganisms promote Bio-P accumulation at the beginning of pedogenesis by regulating PCGs and typical microbial community construction. These findings provide new insights into the mechanisms by which microbial communities regulate phosphorus dynamics during pedogenesis, particularly on newly exposed land resulting from global change in alpine and polar regions.