We present a novel method to phase lock two lasers with a controllable frequency difference. A microwave frequency-modulated vertical-cavity surface-emitting laser is used to phase connect two diode lasers by a two-step injection locking. The phase fluctuations of the two lasers are measured to be 6.4 x 10(-4) rad2, corresponding to 99.94% phase coherence. The frequency difference of the two lasers is tunable up to tens of gigahertz. The sideband suppression of the slave laser is more than 30 dB at 30 microW seed power. A narrow linewidth spectrum of coherent population trapping in rubidium is achieved using such beams.