In　traditional　low　bit-rate　speech　coding,　considering　that　ears　are　not　sensitive　to　phase　information,　the　phase　information　is　often　neglected,　and　this　will　result　in　coarse　and　harsh　speech　quality,　and　it　even　may　lead　to　inflection　in　pitch.　In　order　to　obtain　a　high-quality　speech　codec,　the　phase　information　of　speech　should　be　included　in　codec.　In　this　paper,　the　phase　redundancy　is　reduced　further　based　on　the　dispersion　phase　vector　quantization　method.　In　the　waveform　interpolation　(WI)　speech　coding　model,　the　difference　of　SEW＇s　phase　spectra　of　conjoint　frames　is　quantized　using　predictive　vector　quantization.　The　result　of　this　scheme　reveals　that　the　speech　quality　is　improved,　and　its　naturalness　and　articulation　are　increased　greatly.　Subjective　A/B　listening　test　indicates　that　the　reconstructed　speech＇s　quality　of　this　method　is　better　than　that　of　fixed　phase　with　4-6　bit.　Compared　with　the　dispersion　phase　vector　quantization　method,　the　synthesis　speech　is　slightly　improved　for　female　speakers.