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We propose and numerically analyze a kind of terahertz (THz) phase-shifted gratings based on circularly symmetrical subwavelength waveguides. The filtering principle lies in that through introducing periodically structural disturbance to the subwavelength dielectric wire along the THz wave propagation direction, the coupling response are inspired. By modifying the central period unit to introduce a π shift, a THz phase-shifted grating which can operate as a narrowband pass filter is realized. The extinction ratio (ER) and full-width half-maximum (FWHM) of the phase-shifted grating that offers narrow transmission peak are 12.8 dB and FWHM of 2.0 GHz, respectively. Thanks to the circularly symmetrical structure of the waveguides, the proposed gratings are polarization insensitive. Moreover, the application of phase-shifted grating in refractive index sensing is also investigated. The proposed gratings may pave the way for various applications in compact and robust THz sensing, imaging, and communication systems.