There were two technical phone interviews.

The interviewers were extremely nice and, after the interview, let me ask any questions I wanted.

I would follow the slides they give you for preparation, as well as doing some prep questions from HackerRank.

The first interview started with some questions about my background.

There was a technical question about entering a number and returning an alphabet character. I made the function, but then he told me that he wanted me to use binary conversion in the function, which I forgot how to do.

The second interviewer went right into the question about the deletion of a binary tree.