A differential phase Doppler radar sensor with multiple receivers to remotely detect human vital signals is proposed, which can reduce common-motion artifacts as well as common noises to receivers. This is achieved by differentiating two phase signals from a pair of collocated receivers. Random motions are decomposed into several kinds of motions with respect to the transmitted beam direction. Six differential phase signals are obtained from the four receiver combinations, among which at least one pair can get vital signals with reduced common motion artifacts. A weighted-sum method is proposed to combine six differential signals effectively, which allows vital signals to be clearly detected even with large random body motions. A sensor is implemented with a commercially available 24-GHz radar front-end chip with one transmitter (TX) and four receivers (RXs) to verify the differential phase radar concept. An experiment demonstrates that body motion noises are reduced by over 20 dB with the proposed differential phase radar with multiple receivers.