We experimentally reveal the potential security risks for chaotic semiconductor lasers caused by time-delay signature (TDS). In order to eliminate TDS and enhance effective bandwidth, we propose a new scheme by introducing phase-modulation injection using Gaussian noise or pseudo-random binary sequence (PRBS) as phase-modulation signals. Our numerical results indicate that TDS elimination and bandwidth enhancement are obtained over a wide-parameter region of injection strength and frequency detuning. We further improve the scheme by using two channels of chaotic lasers to generate phase-modulation signals. Numerical simulation results show that the improved scheme is feasible, and TDS cancellation quality is always excellent in wide phase-modulation depth ranges.