I haven't done this before but I heard that telephone interviews are challenging since you don't see the person that you are talking to and that could make it a bit more difficult to convey your motivation. I would recommend to try to sound excited and motivated for this opportunity and try to keep that throughout the interview. For your answers, try to have a clear structure - the STAR (Situation - Task - Action - Result) technique is a good one to follow generally for interviews. Also, I would advise to get write down your experiences and what you learnt from them so that it is easier to talk about them.
If you want to apply later for a vacation scheme, you will deal with similar interviews and assessment centres. I know that there is this course provided by Commercial Law Academy "preparing for interviews and assessment centres", which details the exercises you will encounter during an assessment centre such as group/negotiation exercises as well as what questions you might encounter during the interviews and how to prepare for them.