If your man is constantly on his phone -- relax, it's not always a sign for a red flag.
I've learned over the years that going through a man's phone will get you nowhere. They say, 'if you go looking for something, you'll find it' and that's more than likely the truth. What's done in the dark, will always come to light -- so why waste your time playing Inspector Gadget when you can use your time wisely and be an amazing girlfriend?
Snooping around takes way too much time and energy that none of us really have. If you have the energy to constantly go through someones phone, you should use that same energy and remove yourself from the situation.
Drake sang about "Trust Issues" and they're never wrong. If you can't trust someone now, you'll probably never be able to trust that person. Save yourself the worry and go on about your business. Of course we all get that urge now and then, but in the end is going through your man's phone a good idea? That was a rhetorical question.
You can't enter into a relationship and create a bunch of unrealistic rules. If they were using their phone to text before you two got together, they will text while you are together. That's life. If he was man enough to ask you to be his lady, trust him enough to believe that he's man enough to respect you and not cross any boundaries.
As women, we tend to think a lot -- we can't help it. But, don't let overthinking ruin something good.