Although stable perovskite phosphors, i.e., CsPbBr₃/Cs₄PbBr₆, were extensively reported and made great progress, achieving strong photoluminescence (PL) energy outcoupling remains challenging owing to their short Stoke’s shift with serious PL energy absorption. This study utilized internal resonant scattering (IRS) to improve the PL energy outcoupling (PEO) of CsPbBr₃/Cs₄PbBr₆ perovskite phosphor, which was realized by the nanopore-packing perovskite particles (NP-PPs) structure inside a phosphor. The nano-porous matrix hybrid solid–liquid interfacial reaction was developed to construct NP-PPs in a phosphor, and it is optimized to achieve a denser NP-PP structure with an enhanced PEO effect (2.8-fold enhanced PL intensity). Numerical results revealed that the NP-PP structure transforms the PL energy absorption mode to the IRS mode, most of the scattering PL energy evades NP-PPs instead of propagating inside. The optimized phosphor was applied to white devices, and we finally achieved an ultrahigh luminous efficacy of 131.32 lm/W based on green perovskite phosphors. This study provides a general guide for efficient perovskite phosphors utilizing the nano-porous matrix to enable the IRS effect.