Phase huh? Well you are sampling the RF signal at the LO rate, so the phase information is based on when the LO sine wave hits its peak...that is approximately when the sample happens. But since the output IF frequency is not zero...what exactly does "phase" mean to you? You can put in a constant RF, and constant LO, and you will get out a varying sine wave low frequency output.
You CAN have an unknown RF signal received in one channel, and a known RF sample signal sampled simultaneously in a 2nd channel (sharing the same coherent LO), and infer some things about the unknown RF signal's "phase"