When I had my interviews for PhD (about 5 years ago now but I can't imagine much has changed) they were all fairly standard - why do you want to do a PhD, what interests do you have in the subject area, what do you think are your strengths and weaknesses, what are you hoping to get out of a PhD.
The "why do you want to do a PhD" is particularly common - I had a lovely cheesy line about "not just looking for answers, but looking for new questions".