J.B.
Having a cell phone NOT in a bedroom at night is part of good sleep hygiene and good practice for adults as well so I think you should continue with this practice from that perspective (and hopefully you and your husband follow the same practice - if not, get a regular alarm clock and move your phones to a common charging area outside of your bedroom as well). My oldest son is graduating next week and once he got into the habit of using his phone as an alarm at around age 15, it wasn't worth the fight of making him hand it over anymore so he does have his phone all night but is normally dead asleep by 11 or 12 PM on a school night so it's not an issue.
When my younger sons get phones, I'll use the nightly turn in from the get-go to set the standard for good sleep hygiene. The lure of the glowing screen is just too much for many kids and there are many articles out there that support that it's a good idea for everyone to leave their phone charging in a separate room at night.
I would ask her for what time she thinks is reasonable for a turn in. I think midnight makes sense but she what she says.