iPhone 6s Plus won’t update. Currently iOS 12.5.5
My daughters phone will no longer update.
iPhone 6s Plus
Question marked as
If you are on iOS 12.5.5, then it's not a 6s Plus, it's a 6 Plus.. and it cannot be updated any further
If you (or your daughter) needs to run newer iOS, a newer iPhone model will need to be purchased.
If you go this route.. make sure, at a minimum, to get an iPhone 8 because the iPhone 6s & 7 will not accept iOS 16 this fall.