If the only thing he used his phone for was NFL business it might be reasonable, but there is a lot of personal data on that phone.. should he blindly believe that no one will misuse the information???
Brady is a private citizen first, who plays in the NFL....
Just because he did not turn over the phone does not mean he did not cooperate, and the NFL wants to push this to an arbitrator or judge... that will be good for a few belly laughs..