The phase term in source settings is the initial phase. I guess it is different from the phase what the Stokes parameters. The monitor gives you frequency-domain CW Ex,Ey and Ez (and H components also if you want), so you have the basic quantities and therefore you can calcualte whatever quantities you want, from your definition.
https://spie.org/publications/fg05_p12-14_stokes_polarization_parameters?SSO=1
We have an online example for periodic simulation Calculating the far field polarization ellipse – Ansys Optics
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