  We report temperature-dependent reflectivity spectra of the layered van der
Waals magnet CrSBr in the far-infrared region. Polarization-dependent
measurements resolve the vibrational modes along the E$\|a$- and $b$-axes and
reveal the clear structural anisotropy. While the $a$-axis phonons notably
harden on cooling, the $b$-axis phonon frequencies are almost
temperature-independent. A phonon splitting due to the antiferromagnetic phase
transition is observed for the 180~cm$^{-1}$ $a$-axis vibrational mode,
accompanied by a phonon softening below $T_N$. Furthermore, an additional mode
with strong magnetic characteristics at $\sim$360~cm$^{-1}$ is identified and
attributed to the magnon excitation of CrSBr.
