Measuring phase shift

I designed MEMS phase shifter and am now observing the phase shift by checking S(2,1) parameter -angle degree. Is this correct and can I observe the change in phase in HFSS?

you can estimate phase shift by simulating ANG [S21], but ONLY if your phase shifter is impedance matched to 50 ohms. IF you have a poor return loss, the estimate for ANG [S21] will also be impacted by load and source impedances...