A bi-directional ROF system based on double-sideband with optical carrier suppression (DSBOCS) scheme to generate optical millimeter-wave signal via electronic-optical phase modulation (EO-PM) was demonstrated.The communicated bandwidth could be doubled to realize Ultra Width Band & Ultra High Frequency (UHF) communication via phase modulation.The BERs of downlink and uplink via adjusting the phase deviations of the phase modulators could be successfully controlled.The simulation result shows that the bi-directional 2.5 Gbit/s data modulated with a 24 GHz UHF microwave in a light beam with a transmitted power of 3 dBm is successfully transmitted over a 40 km SMF-28 fiber with an attenuation of 0.25 dB/km and a dispersion of 20 ps/(nm·km).