A new microwave photonic phase shifter is presented. It is based on an optical single-sideband modulator and an optical phase shifter inside a Sagnac interferometer. It relies on the use of the novel nonreciprocal optical phase shifter to obtain an optical phase shift, which converts into an RF phase shift. The microwave photonic phase shifter has the advantages of realising a continuous 0-360° phase shift on microwave signals using off-the-shelf components and only requiring a single control. It also has a compact structure and robust performance. Experimental results are presented, which demonstrate 0-360° phase shift of microwave signals over a sub-octave frequency band.