Problem is that instantly replacing said phone does not teach the right lessons to the kid either.
I first gave my son a mobile phone when he was about 10, when he started at a distant school involving taking public buses to get there. It was an old brick (late '90s nokia), and attached by a string to his schoolbag for the first few years. Even so, he still managed to lose it a couple of times (fortunately we always recovered it, even if it took several weeks).
Now at age 15 he's pretty good about it, so he gets a modern smart phone.