To address the additional energy consumption, inherent low radio frequency gain, and higher multi-wavelength channel crosstalk interference faced by intensity modulation and direct detection (IMDD) optical link in analog mobile fronthaul (A-MFH), this paper proposes a phase modulation and direct detection (PMDD) optical link scheme based on the Mach-Zehnder interferometer (MZI) to replace the traditional IMDD. In this scheme, optical phase modulation (PM) instead of intensity modulation (IM) is used in the optical transmitter, and wideband, high-linearity PM-to-IM conversion is achieved in the optical receiver using an unbalanced MZI, which enables the direct detection of phase information in the optical receiver. Extensive numerical simulation results show that when 12 channels of 100-MHz 64QAM-OFDM signals in A-MFH are transmitted synchronously over 20 km of standard single mode fiber, the optical receiver sensitivity in the PMDD optical link based on MZI achieves a 4.2 dB improvement compared to the IMDD optical link. Furthermore, the frequency response roll-off effect of the system is effectively compensated by adaptive power loading to balance the achievable performance among the 12 channels.