@justanotherbutterfly
I've tried to link in this reply a reddit post that I found very helpful for my first phone call interview (which went kind of rough - she asked for my research interest at the school and I said I didn't have anything specific in mind yet and would like to tailor my interests to the needs of the population in the school's state. I had 15 minutes notice for mine so the interests I gave might have been too general!). I think familiarizing yourself with the recent lab projects and publications can also help more than just reading the professor's papers. I would also look on the lab page and check on the goals of the lab students for your PI - you don't want to have a career goal that deviates significantly from what the school can provide (I didn't get a chance to do this before mine and I kind of regret it. My career goals are malleable but I think faculty like to see students who have something set in mind - usually academia is what I answer). A lot of the 30 minutes will be spread between answering questions, general banter, etc. And just be sure you have at least one question to ask them if you can, I think it shows more initiative. Good luck!