Hey Gayle, I concur with Tricky's comments.. the things you will have to demonstrate more strongly are reasons for wanting to do a PhD (and here you will have to have some idea about the PhD process, challenges etc.,), and that you have the enthusiasm and determination to see it through to the end.

Intellect, and to a lesser extent subject knowledge, are all assessed from your CV/degree result and proposal respectively. My guess is if you have been selected for an interview you have passed the latter requirements more or less. Always helps to read up on the departments/supervisors research interests and round your area.

Good luck