I suspect it's single sideband, but I'm not sure (I've never used it). It's for analysing transient results, and is defined this way:
Calculates the transient phase noise of the input waveforms in
decibels (dBc/Hz). Phase noise is defined as the power spectral
density of the absolute jitter of an input waveform.
You tagged this post with lots of terms like pss, pnoise etc - so you would not use this function if you're using pnoise. You'd use the pn() or phaseNoise() functions, and these will give you the single sideband phase noise (strictly the output noise in dBc if using "sources"). You'd be better off using "modulated" pnoise and then you can get either from the direct plot form.