Although phosphorus exhibits a high lithium uptake, its poor cycling performance and low coulombic efficiency limit its application for lithium-ion batteries. Herein, ex-situ solid-state 31P and 7Li NMR studies together with XRD measurement are performed to provide a deep insight into the amorphous Li-P alloys and amorphous-to-crystalline transformation process. The amorphous Li3P and overlithiated Li3+xP phases are firstly experimentally detected. The evolution and coexistence of various Li-P alloys intermediates including overlithiated Li3+xP upon lithiation, and the recovery of the Li-P alloys intermediates to the initial phosphorus after delithiation are observed. Our results also disclose for the first time that partial LiP7 phase and Li3PO4 resulting from slight surface oxidation of rP still retain at the end of charge, which are highly relevant to the low coulombic efficiency in the first cycle and the successive decay of the performance. This study provides some insights into the specific multi-phase evolution mechanism of alloying anodes that may be generally involved in conversion-type electrode materials for Li batteries.