I have to agree with Adam. I'm a female, and while I think people are entitled to SOME privacy, I think it's pretty crummy that she seems to be hiding something from you.
Personally I hate the ideas of these stupid phones. While they're good in an emergency, they sure create problems such as this.

It's too easy for spouses/partners to play little games.
I'd ask her what she's hiding. If she won't tell you, you have your answer. If she says "nothing" then ask to see her phone. If she won't LET you, you STILL have your answer.
I'm sorry you're in this spot. I wish you the very best. God bless and let us know how things turn out, okay? God bless and please take care. Hugs, Lee