Can individual photons be measured for polarization and phase or is there a similar limit that requires more than one photon to do so? I suppose both are relative to some previous polarization or phase?
Polarization can be measured using polarization filter and light detector, but it is destructive in the usual sense of quantum theory. That is, if the detector after polarization filter clicks, we know the EM field had non-zero component in the direction of the filter, but we do not find out the other components it had before entering the filter.