Phosphorus (P) is essential for life. We studied microbial processes driving the P cycle in soils developed on the same rock but with different ages (0–100 years) in a cold desert. Compared to previous studies under cold climate, we found much slower weathering of P-containing minerals of soil development, likely due to aridity. However, microbes dominate short-term dynamics and progressively redistribute P from the rock into more available forms, making it available for plants at later stages.