Abstract: As the human ear is dull to the phase in speech, little attention has been paid to phase information in speech coding. In fact, the speech perceptual quality may be degrated if the phase distortion is very large. The perceptual efiect of the STFT phase spectrum is studied by auditory subjective tests in this paper. Three main conclusions are: (1) If the phase information is neglected completely, the naturalness of the reconstructed speech is very poor; (2) Whether the neglected phase is in low frequency band or high frequency band, the difference from the original speech can be perceived by ear; (3) The human ear can not perceive the difference of speech quality between original speech and reconstructed speech while the phase quantization step size is little than π/7.