The Raman scattering response of the biaxial antiferromagnet ${\mathrm{CoPS}}_3$ has been investigated as a function of both magnetic field and temperature. The peaks observed in the low-frequency spectral range $(90–200 {\mathrm{cm}}^{-1})$ have been identified as hybrid magnon-phonon excitations. The energies of the bare magnon and phonon modes and the effective coupling strengths between different excitation pairs have been determined. The strong and selective magnon-phonon interaction largely accounts for the pronounced splitting of two phononlike modes observed at 152 and 158 ${\mathrm{cm}}^{-1}$ in the antiferromagnetic phase of ${\mathrm{CoPS}}_3$. Based on the identification of bare magnon excitations and their magnetic-field dependence, we propose an updated set of parameters for the effective exchange $(J_{\mathrm{eff}}=9.9 \mathrm{meV})$ and biaxial magnetic anisotropy $(D=4.3 \mathrm{meV} \text{and} E=-0.7 \mathrm{meV})$ and advocate for an apparent anisotropic $g$ factor $({\mathrm{g}}_x\hspace{0.17em}=\hspace{0.17em}{\mathrm{g}}_y\hspace{0.17em}=\hspace{0.17em}2, {\mathrm{g}}_z=4)$ in the ${\mathrm{CoPS}}_3$ antiferromagnet.

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• High magnetic fields
• Magnetic anisotropy
• Magnetic order
• Spin dynamics
• Spin-phonon coupling