This paper proposes and numerically studies a scheme of chaos generation in semiconductor lasers with random-digital-phase-modulated optical injection. The simulation results demonstrate that as the modulation rate or modulation depth increases, the laser state changes from injection-locking to chaotic through a quasi-periodic route due to the excitation of undamped relaxation oscillation by the phase change. Chaotic laser with an effective bandwidth over 10 GHz can be generated by random-digital-phase-modulated optical injection. Given the anti-interference capability of digital signals in long-distance transmission, the proposed scheme provides a new approach for long-distance chaos synchronization and key distribution.