β-FeSi₂, an environmentally friendly and high temperature oxidation-resistant thermoelectric material, has potential applications in the field of industrial waste heat recovery. Previous studies have shown that phosphorus (P), an ideal n-type dopant in the silicon (Si) site of β-FeSi₂, can easily lead to the formation of a secondary phase, thereby limiting the enhancement of thermoelectric performance. In this study, a series of FeSi_2-xP_x (x=0, 0.02, 0.04, 0.06) samples were synthesized using an induction melting method, which greatly inhibited the formation of the secondary phase. Then, the influence of P doping on the electrical and thermal transport properties of β-FeSi₂ was studied. The results indicate that the solubility limit of P in β-FeSi₂ is about 0.04, consistent with earlier theoretical predictions based on the defect formation energy. It is also discovered that P doping enhanced the thermoelectric performance of β-FeSi₂, culminating in an optimal figure of merit (ZT) of FeSi_1.96P_0.04 approximately 0.12 at 850 K, which is much higher than the previous results (ZT about 0.03 at 673 K). However, compared to β-FeSi₂ doped with other n-type elements like cobalt (Co) and iridium (Ir), which can achieve carrier concentrations up to 10²² cm^-3, P-doped β-FeSi₂ exhibits lower carrier concentrations, with the highest of only 10²⁰ cm^-3. This results in a weaker electron-phonon scattering effect, which in turn constrains the overall enhancement of the thermoelectric performance. If the carrier concentration could be further increased, the thermoelectric performance of the material is expected to evolve significantly.