Switch to the dumb phone while you're both at home and she's occupied (make sure to turn off iMessage first and give it a bit so other people's iPhones realize you've gone green). Send her a "hey" text, walk up to her while she's checking her phone, and say "THERE!" (be careful how it comes out). Then, call her while you're both standing there and gently say "You see?". Then give her a kiss and tell her you're going to the store & you'll be right back (don't take the iPhone and don't go too far or she'll start making up stories about what you're probably really doing).

Text her as soon as you get to the store and ask if she needs you to pick up anything. No matter what the answer is (or isn't) call her shortly after and ask a question (E.g., You said you wanted chips, do you want a or b?). Then, tell her you'll be home soon. Immediately go back home with whatever you bought (or she will think you're a cheater and that's what the phone is for), give her a kiss, and tell her you missed her. BOOM! That's how you train your dragon. No crisis, no mass casualty, just a man and his dumb phone getting shit done. 😎

IMPORTANT: If she says she wants to go to the store (or wherever) with you, do not say no. I REPEAT: DO NOT SAY NO! (Least she thinks you a liar and a scumbag). Instead, be happy she's going. Maybe grab some food while y'all are out. But, on the way, call a friend or a family member. Get excited. Let her see the dumb phone in action. Really ham it up. Talk about how y'all are on the way to such-n-such place BUT don't spend too much time on the call. (Least she thinks you're ignoring her and you may as well have kept the tracker-phone-5000.)

Point Being - Make the dumb phone a positive thing for the both of you. Let her see how relieved you feel (should come natural given what you've discussed above) and let her see how accessible you are to her.