The vibrational properties of $mathrm{CrI_3}$ single crystals were investigated using Raman spectroscopy and were analyzed with respect to the changes of the crystal structure. All but one mode are observed for both the low-temperature $Rbar{3}$ and the high-temperature C2/$m$ phase. For all observed modes the energies and symmetries are in good agreement with DFT calculations. The symmetry of a single-layer was identified as $pbar{3}1/m$. In contrast to previous studies we observe the transition from the $Rbar{3}$ to the $mathrm{C2}/m$ phase at 180,K and find no evidence for coexistence of both phases over a wide temperature range.
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