Two-dimensional Ruddlesden-Popper （RP） layered perovskites have received lots of attention in recent years due to their excellent optoelectronic properties and good environmental stability. Their unique properties make them ideal candidates for applications in solar cells， light-emitting diodes， and X-ray detectors. However， two-dimensional RP-type layered perovskites synthesized by solution methods typically exhibit mixed phases with random inorganic layer numbers （i.e.， multiple n-values）， which hinders their application. In this study， the crystallization process of RP layered perovskites was regulated by replacing BAI with BAAc to achieve effective phase purification. The enhancement in phase purity was confirmed by characterization methods， and the phase-purified perovskite material exhibits reduced defects. Consequently， significantly improved carrier extraction and transport capabilities， along with suppressed ion migration were achieved. These structural improvements directly enhanced the performance of the X-ray detectors. The phase-purified detectors exhibit lower detection limits （160.24 nGy_air·s^-1） compared to the unpurified devices， demonstrating stronger capability in low-dose X-ray detection. Additionally， the phase-purified device shows good irradiation stability. Therefore， phase purification not only effectively improved the detection performance of two-dimensional perovskite X-ray detectors but also enhanced device stability， proving the broad application prospects of phase-purification technology in perovskite X-ray detectors.