What title do you hold after you've defended but before you graduate?
There isn't a formal, universally accepted title here. The general standard has been to call them "Doctor" since everything else is in principle a formality.

The only other note that I'd make is that it's not commencement that makes the student in question a doctor, but rather conferral of the degree by the university. Some universities may confer degrees multiple times per year, but only have one commencement ceremony.

So, I would not include "Ph.D." next to my name, but in the education of my CV, I'd write "Ph.D. (to be conferred Month Year)," as that is entirely accurate representation of the state of affairs.