We adopted a chemical substitution strategy to design a particular anionic structure with large optical anisotropy in phosphate. Specifically, we replaced one O2- in Ba3P3O10Cl by two Cl-, leading to the formation of a new compound of BaPO3Cl (P2(1)/c). Notably, this compound is the first metal phosphate chloride featuring infinite [PO3](infinity) chains, and it displays good chemical and thermal stability, as well as a short UV cutoff edge (<200 nm) and relatively large birefringence.