In this work we analyze the temperature dependence of the coherent phonon dynamics reported previously in Ref. 18. Fig. shows the periodic modulations observed in the ultrafast differential transmission experiment (details in ESI † ) by photo-exciting the free carriers at 3.06 eV with a train of ultrashort optical pulses and at sample temperatures ranging over 5-100 K. Note that no first-order phase transitions are present within this temperature range . These periodic modulations of the optical absorption of the sample are the signatures of coherent phonons generated by resonant impulsive stimulated Raman scattering (RISRS) . The ultrashort optical pulse generates a coherent wavepacketa superposition state of phonon modes that are excited with common phase. The intensity of transmission modulation reduces with time due to the dephasing of the coherent phonon population. The dephasing rate becomes faster at higher temperatures, indicating that the scattering with the thermally generated incoherent phonon population is the primary dephasing mechanism. The RISRS spectrum at 5 K, shown in Fig. , is obtained by taking the Fourier transform of the time dynamics (temperature dependent RIRS spectrum is shown in the ESI † ). Two dominant phonon modes are clearly observed, labelled M1 at 2.61 meV and M2 at 4.40 meV, in addition to a few modes between 5-6 meV. All the observed phonons have been previously assigned to the lattice vibrations predominantly within the lead iodide layer . Specifically, M1 and M2 correspond to octahedral twisting along one of pseudocubic axes and octahedral twist and Pb-I-Pb bending, respectively (see Ref. 18 for details of the assignment).