Some (probably obvious) tips for anyone doing PhD interviews from someone who’s just gone through them and got one (but I also wish I had really considered these points beforehand):
1. Have a response planned for when you don’t know the answer to the question, and one that shows you’re considerate of the topic. Like ‘I would need to check that, as the research I’ve read focuses on x and y’. Also useful to have something similar ready if you actually do know the answer but your mind is blanking and you need a moment to recall.
2. In knowing your field try to have an approximate knowledge of as much as possible, like choosing to at least minimally cover details you decide are irrelevant. I presented a paper in an interview, (and chose one which was complicated and maths heavy from my background) and only just got through some of the questions as they all turned out to be 100% technical.
3. With having an understanding of a PhD, and specifically the trials and errors, have an answer to how you would handle frustrating work. If you’ve thought through that scenario you get the answer to a couple different questions, like what qualities are expected of a PhD student (perseverance, problem solving, adaptable), how you would respond to your research if/when it gets in a rut, and potentially improve your understanding of how PhD research actually works (like how if you really can’t solve a problem, what happens to your PhD then?)