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 1 300 ℃, with Fe₃P added into the FeNiCo-C system. The synthesized diamond samples were characterized by Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, photoluminescence (PL) spectroscopy, and X-ray photoelectron spectroscopy (XPS). With increasing Fe₃P addition, the diamond color gradually lightens, and the crystal morphology changes from octahedral to hexoctahedral. Moreover, the addition of Fe₃P alters the catalyst properties, leading to the increases of nitrogen solubility of the catalyst. Thus, fewer nitrogen atoms enter the diamond lattice, resulting in a decrease of nitrogen impurity content in the diamonds. Phosphorus doping increases internal stress and induces lattice distortion in the diamond crystal, resulting in degrading of the diamond 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, and supports potential applications of phosphorus-doped diamond crystals.