I’m fully on board with pretty much everything @vcdgrips wrote.
I didn’t do the “rock” thing with my boys, but all the other stuff is very familiar.
You can limit access to apps with “Parental Controls” on an iPhone. Needs a password or PIN to override or make changes to the limits. You can even set hours-per-day and time-of-day limits on things.
From my experience, it will also pay off to specifically emphasize that, if you’re paying for the phone, you expect texts and calls to be returned, and voicemail to be set up and checked. One son had configured his phone so that it wouldn’t make noise or distract him in school (good plan so far...), but often forgot to change the settings after school and on weekends - making him difficult to contact, but only as a side-effect of good intent.
You’ll know when it’s time to get her a phone (when it’s necessary and helpful to both of you). And it will become evident when it’s smart to allow more access and freedom as she gets older.