Thanks! And congrats on your interview! Interviews can really depend on the professor and the department. I interviewed for the sociology PhD and the geography PhD--very different experiences. For my sociology interview, it was in person and we just talked about overselves and our research interests over tea. My geography interview was a formal Skype interview and the professor grilled me on my research proposal and didn't ask me anything about myself. It was actually pretty clear once I had the geography interview that it wasn't a great fit, so I wasn't surprised when I received a rejection from geography. So, interviews differ, but you'll definitely be asked about your research, so be prepared to discuss your proposal in depth. I'd also try to use the interview as a way to assess fit, because it's as much about your needs and what you want out of a PhD program as it is about their need to admit quality students. Also, since the PhD there is basically a three-year independent study, it's important to make sure that your propspective supervisor is someone who you not only would want to work with, but who will also support you and who will be invested in your success. Good luck!