We introduce phonon recycling (local reabsorption of emitted phonons, especially before their inter-phonon interactions leading to equilibrium occupancy) in devices.Phonons are emitted in all resistive and energy conversion processes in solids and are generally called the waste heat,presenting efficiency loss. We discuss in-situ (at/adjacent to the emission site) recycling of optical phonons to improve thermal management (lowering operating temperature and/or reducing net heat generation) and to increase efficiency. We consider photon-assisted and unassistedphonon absorption, and introduce phonon-recycling in designed (using ab initio and mesoscale treatments of kinetics) layered structures. These layers are placed adjust to the phonon emission sites, with thicknesses and compositions matching their assisted and unassisted phonon absorption function. Phonon recycling application examples include high-power lasers and transistors, and phonon voltaic.