Pristine GeTe is a highly degenerate semiconductor shows very low thermoelectric properties due to its large carrier concentration induced by the presence of Ge vacancy. In this work, we report a promising thermoelectric figure of merit (zT) of ~1.8 at 700~740 K was obtained on high-quality Ge1-xSbxTe crystals grown by the Bridgman method. The substitution of Sb into Ge sub-lattice significantly reduces the excess hole concentration due to the donor dopant nature of Sb. The zT enhancement can be attributed to the reduction of carrier density due to Sb doping, as well as optimizes the electrical conductivity which subsequently enhances the Seebeck coefficient in Ge1-xSbxTe compared to the pristine GeTe crystal. Reduction of thermal conductivity arises from enhancing phonon scattering by Sb doping effect, which results indicate that Sb doping is effective for enhancing the thermoelectric performance in p-Type GeTe Compound. With the inelastic neutron scattering investigation of selected Ge1-xSbxTe crystals, the significant difference on phonon dispersion relation is investigating.