Two new phosphates-Cs6Mg6(PO3)(18) (CMP) and Cs2MgZn2(P2O7)(2) (CMZP)-have been obtained, using high-temperature molten methods. Crystals of CMP with the polar P2(1) space group display a new three-dimensional (3D) anionic framework possessing two one-dimensional (1D) [PO3](infinity) chains that are interconnected by isolated MgO6 octahedra, while CMZP with centrosymmetric monoclinic space group P2(1)/c possesses a new [MgZn2P4O20](14-) structure unit consisting of two isolated P2O7 dimers, one ZnO4, and two disordered Mg/ZnO4 tetrahedral units. The polar phosphate CMP with deep-UV transparency (below 190 nm) shows weak second harmonic generation (SHG) response (0.1 x KDP), and the dipole moment analysis suggests that the weak SHG response mostly originates from much distorted CsOn polyhedron. Some related properties, such as optics, thermostability, and band structure derived from density functional theory, were explored.