A reliable spectroscopic assignment of the high-frequency proton modes in CsH2PO4 (CDP) is possible only within the framework of the fully ordered proton, low-temperature P21 spectroscopic experimental and theoretical data. This proposal aims at the resolution of these complexities by accounting for the lattice dynamics-simulated directional H-apVDOS along the three Cartesian axes of CDP, from which the corresponding anisotropy of theADP tensor can be deduced. It is proposed, to address this problem by combining ab inito simulations and single crystal diffraction measurements of the FE and PE phases of CDP.