I just had my PhD interview, and key questions I got were about the theoretical and practical implications of my project. Like, how will it effect/have an impact on the current scholarship of the PhD's field? they want to know not just that you know your stuff, but that you can critically and realistically think ahead. I wouldn't make any outlandish claims, but you can reason out a lot of your answers. And no ********ting - it's better to acknowledge that you don't precisely know how you would go about doing this or that aspect of the project, since you haven't studied/got experience in that area yet, but that from your current understanding you would study this/get training in that/ follow key approaches moving forward etc.
One of my key questions was how, if I had to start now, would I go about curating the exhibition at the institute? and I started out by saying that I would first study similar displays by the institute, in order to make sure I could match the style and voice of the institute, to make sure I was representing it in a way that was in line with their current work. and then went on to say how I would follow the guidelines I learn about curation in my Masters, and talked a bit more about relevant audience and critical engagement etc. So I feel that a lot of a PhD is not just knowing your stuff, but knowing how to apply yourself. obviously they're not expecting me to be able to have a complete answer for this question, since my study of the project hasn't even begun. But the key here is to show that I have the foundation and capability to engage with the topic in the areas they are interested in. Does that make sense?
And show that you're interested in the topic beyond the scope of the PhD - that you'd be interested in/studying the topic regardless of the PhD. They're looking for a candidate that has the interest and motivation to see the whole project through, so your main motivation can't just be to get a PhD.
Also - try not to think about it as an interview! This is just a chance to nerd out about a topic you're passionate about, with other people who are also really interested in talking about it. Just show honest enthusiasm and a willingness to learn and you'll do great!