Copper(I) phosphide (Cu3P) with high theoretical capacity and metalloid characteristics performs great potential as chloride ion (Cl−) storage electrodes in chloride-ion batteries and deionization. However, the unsatisfactory electrochemical performance of Cu3P due to the sluggish rate and poor stability severely limited the development of practical application in electrochemical Cl− removal. Herein, monolithic low-tortuous Cu3P nanorod arrays (mCu3P NA) have been fabricated through sacrificial template array engineering combined with the controlled phosphating strategy. Benefiting from the low-tortuous array structural advantages involving rapid charge transfer and plentiful active sites, the resultant mCu3P NA electrode exhibited excellent areal deionization capacity (2.21 mg-Cl− cm−2 at 1.6 V) and corresponding fabulous rate (0.074 mg-Cl− cm−2 min−1), which was superior to previously reported electrodes in electrochemical deionization. Furthermore, the phosphating degree could adjust array architecture and component of Cu3P/Cu heterostructure, thus affecting areal deionization performance. In addition, the mechanism of Cl− capture by Cu3P was first elucidated, related to the redox of P3−/P0 and the formation of CuCl. These findings unlock the potential and elucidate the mechanism of Cu3P for electrochemical Cl− removal, as well as provide a new idea for rational design of high-performance array electrodes for environmental applications.