In reply to Jay815:
I don't think there's any way to specify a phase shift on a port for s-parameter analysis. The only parameters on the port you have to control the phase are the phase parameter (which along with the mag parameter specify the size of the AC input - this is only used for ac analysis - there's also pacphase which is used in the pac, hbac and qpac analyses), and the sinephase parameter which is only used in time-varying analyses (e.g. tran).
So that's why it doesn't work - it's not a bug, but since you're not injecting a signal in sp analysis, I'm not sure it really makes sense.
In reply to Andrew Beckett:
For the first question, the "phase for Sinusoid" is only relevant when you are generating a sinusoid - so in large signal analyses such as tran. For sp analysis you are not generating a large signal sine wave, so this is not used.
For the second question I am not the right person to ask - it's been a long time since I was last testing designs on the bench (18 years?) - apart from the odd hobby thing at home, and even then not sure I ever used a VNA.
Thank you very much for your help and quick answer! Now I came to know more about Spectre SP simulation. :)