A phase-encoded photonic analog to digital conversion (PADC) based on phase modulator is presented, which can avoid the effects of the bias voltage drift and two-arm asymmetry in intensity modulator on the performance of PADC. The theoretical model of the PADC is built. The condition to realize ideal phaseencoded PADC based on phase modulator is obtained. The effect of polarization state, amplitude and time jitter of optical sampling clock on the system performance is analyzed. The results show that the presented scheme can restrain the effect of optical sampling clock amplitude jitter, and its effective number of bits (ENOB) can be more than 10 bit in the case with reachable control precision. The feasibility and the validity of the scheme are verified by a single-wavelength system experiment with a sampling rate of 583 MS/s. The ENOB, which is 6.38 bit, is enhanced more than 2 bit by adopting phase-encoded scheme.