Ideally, it needs to be signed off by an institution that your local passport office accepts. For my latest UK passport, I had to send off the real PhD certificate and it came back within 10 days. My friend (also UK citizen) got his PhD from University of Warsaw and it took months to verify. I am not sure what that process was but the issuer of the PhD is important if you want it legit.
Only my first ever job out of uni checked that I did a PhD there, nowhere else has.
In the UK, the passport appears to be the root ID, so all other renewals check that (driving license is the only other one I've done recently).
I think @edent's answer is best: PhD by publication is best - then bind them together with intro (which can be a survey paper), conclusion and any additional references. I know a Comp Sci PhD did this recently (2016?) at UK uni. Cracking PhD it was too.