Abstract: To investigate the effects of phosphorus doping on diamond crystal growth, diamond single crystals doped with phosphorus were synthesized along the (111) plane using the temperature gradient method. The experiments were conducted under conditions of 5.5 GPa and 1300 ℃, with Fe₃P added into the FeNiCo-C system. The synthesized diamond samples were characterized by Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, photoluminescence (PL) spectroscopy, and X-ray photoelectron spectroscopy (XPS). With increasing Fe₃P addition, the diamond color gradually became lighter. The crystal morphology changed from octahedral to hexoctahedral. The nitrogen impurity content in the diamonds showed a decreasing trend as more Fe₃P was added. This occurs because the addition of Fe₃P alters the catalyst properties, increasing the nitrogen solubility of the catalyst. Thus, fewer nitrogen atoms enter the diamond lattice. Phosphorus doping increases internal stress and induces lattice distortion in the diamond crystal, degrading its quality. This conclusion is supported by the shift and broadening of the Raman peak. The incorporation of phosphorus atoms inhibits the formation of NV⁻ centers in diamond crystals. XPS results confirm the successful incorporation of phosphorus into the diamond lattice. This study provides useful insights for understanding the synthesis mechanism of phosphorus-doped diamond crystals. It also supports potential applications of phosphorus-doped diamond crystals.