I took the DAT two weeks ago and during my 30 minute break, they told me I was free to do whatever I wanted during my break (bathroom, eat, use phone, walk outside, etc.) I of course left my phone in my car just to be on the extra safe side. As I was leaving the testing center (after completing the full exam) some guy (taking another exam) grabbed his phone from his locker and they saw it. He told them he was just checking his emails during his break. They made him give them extra information so I'm assuming they were documenting his cheating (intentionally or unintentionally).
TL;DR My testing center allowed phone usage but there's nothing you're really going to learn and retain in that short 30 minutes.