A similar photophysical scenario can be identified in other derivatives of metal-halide perovskites, including in layered twodimensional systems such as the Ruddlesden-Popper (RP) metal halides . However, given the globally neutral character of excitons that are the primary photo-excitation in these systems, one might expect a diminished role for the Coulomb-mediated polaron coupling . We have previously highlighted, on the contrary, the critical role played by the phonon interactions in various exciton dynamics using a number of unambiguous experimental observations. We demonstrated that distinct excitonic states are distinctly phonon-dressed , elastically scattered and coupled non-adiabatically by the lattice phonons . We have also suggested that the photoexcitations must, in fact, be treated within the exciton polaron framework . As a corollary to this hypothesis, one may expect to perceive the seemingly independent many-body dynamics of phonons in the dynamics of exciton polarons. For example, we consider the thermal dephasing of excitons, which is primarily driven by the elastic scattering of a coherent exciton population with the thermally populated phonons. If the coherent population is that of exciton polarons, then the ther-mal dephasing of phonons (in other words, phonon-phonon interactions driven by the anharmonicty of the polaron dressing phonons) will also contribute to the elastic scattering. The models used to fit the temperature dependence of the exciton dephasing rates or the exciton linewidths do not, however, consider phononphonon scattering explicitly. Moreover, direct observations of the structural dynamics and lattice anharmonicity in RP metal halides are missing.