You should be able to get the phase from the mode expansion monitor. Sometimes, it is hard to get a sense of the absolute phase. In those cases, you can use a narrowband source with multiple frequency points and calculate the relative phase at each point with respect to the phase at central frequency to get more insights into how phase changes over the spectrum.
This might be a useful reference, but the analysis group used in this work (grating_s_params) is applicable to periodic structures only: https://optics.ansys.com/hc/en-us/articles/360042097393-Metamaterial-parameter-extraction-Smith
Ports are a combination of mode source, DFT monitor, and mode expansion monitor. So, you will not be able to inject plane waves into the waveguide using Ports.