We investigated the infrared vibrational properties of pristine and Re-substituted MoS2 nanoparticles and analyzed the extracted phonon lifetimes in terms of multiple scattering events. Our measurements reveal both size- and doping-dependent changes that we attribute to grain boundary scattering and charge and mass effects, respectively. By contrast, Born charge is affected only by size. These findings illustrate the utility of reaching beyond traditional bulk semiconductors and quantum dots to explore how doping and confinement impact carrier-phonon interactions in low-dimensional semiconducting nanomaterials.