We introduce a lock-in method to increase the phase contrast in incoherent Differential Phase Contrast (DPC) imaging. The use of a smart pixel detector with in-pixel signal demodulation, paired with synchronized illumination, provides the basis of a bit-efficient approach to DPC. The experiments show an increased sensitivity by a factor of 8, for equivalent standard DPC measurements; single-shot sensitivity of 0.7 mrad at a frame rate of 1400 fps is demonstrated. This new approach may open the way for the use of incoherent phase microscopy in biological applications where extreme phase sensitivity and millisecond response time is required.