There are at least two interview stages. Your first interview will most likely be an interview with a professor in the admissions committee. In the first interview, you will mainly be asked about your studies and your research interests. The second interview is mainly with the PhD program coordinator. The coordinator asks in-depth questions about why you should come to this school.

Multiple 30 minute interviews with faculty and a current student. Very simple questions you would expect and the faculty are all very nice. I prepared by looking up what each professor's research was about but that information didn't even come up sometimes, but could make for a nice conversation starter if the conversation died down.