Congrats on getting to the interview phase. I've heard horror stories of Microsoft interview process and reluctant to go through their interview meat grinder.
If I remember correctly, the initial phone screen was a joke. They literally just asked me to code fibonacci once, and something similar the other time. All the interviewers themselves were nice to me, etc.
Best interview experience I've ever had. They had me do a quick online thing then come to an event with a bunch of people. No waiting around for weeks between each stage, no multiple phone screens, no waiting for weeks after for a yes/no.