A Bessel function method incorporating carrier modulation is introduced, which accurately determines the phase shift amplitude of vibration signals by analyzing the amplitude relationship between the carrier’s main frequency and its harmonics. Experiments with a programmable signal generator and interferometer probe confirmed its feasibility and superiority over traditional Bessel function methods in weak signal calculations. In the experiment, this method can precisely calculate phase shifts down to 3.9 mrad and achieve a minimum detectable phase shift of 22 μrad, making it suitable for signal calibration in weak signal scenarios and analysis of phase carrier modulation signals.