This　study　investigates　Ga-doped　n-type　PbTe　thermoelectric　materials　and　the　dynamic　phase　conversion　process　of　the　second　phases　via　Cu2Se　alloying.　Introducing　Cu2Se　enhances　its　electrical　transport　properties　while　reducing　its　lattice　thermal　conductivity　(kappa(lat))　via　weak　electron-phonon　coupling.　Cu2Te　and　CuGa(Te/Se)(2)　(tetragonal　phase)　nanocrystals　precipitate　during　the　alloying　process,　resulting　in　Te　vacancies　and　interstitial　Cu　in　the　PbTe　matrix.　At　room　temperature,　Te　vacancies　and　interstitial　Cu　atoms　serve　as　n-type　dopants,　increasing　the　carrier　concentration　and　electrical　conductivity　from　approximate　to　1.18　x　10(19)　cm(-3)　and　approximate　to　1870　S　cm(-1)　to　approximate　to　2.26　x　10(19)　cm(-3)　and　approximate　to　3029　S　cm(-1),　respectively.　With　increasing　temperature,　the　sample　exhibits　a　dynamic　change　in　Cu2Te　content　and　the　generation　of　a　new　phase　of　CuGa(Te/Se)(2)　(cubic　phase),　strengthening　the　phonon　scattering　and　obtaining　an　ultralow　kappa(lat).　Pb0.975Ga0.025Te-3%CuSe　exhibits　a　maximum　figure　of　merit　of　approximate　to　1.63　at　823　K,　making　it　promising　for　intermediate-temperature　device　applications.