30-minute case interview?

So I have an interview with a smallish PE fund ($1.75bn AUM) tomorrow, and they've asked me to complete a 30-minute case interview over the phone with one of the associates. Looking at a lot of the information on PE case interviews, however, it appears almost all traditional ones give you the information ahead of time so you can properly structure out your thoughts and build a presentation--except I don't have anything prior.

So would the best way to prep be to focus on consulting case studies for acquisitions/profitability questions, or is there a more specific path this is likely to go down that I can prepare for more effectively.