I actually really enjoyed the phone interview (it made me want to attend that REU! It seems like a perfect fit for me). He asked me to tell him something about myself not on the application, if I had questions about the REU, and how I work - independently or collaboratively. He told me about his goals for the program, and asked me a bit about my experience in math and what challenges I have faced in math. Overall, it was a really great experience for me to have - I learned so much about the REU. He said he wanted to get a feel of the possibilities for his research team and how we would work together.