We got them smart phones when they went to college. Before that, we gave them a flip phone to be able to communicate with us.
When our two oldest were in HS, they complained about how unfair it was, since all their friends had phones. Later, when many of their friends had life struggles that my children equated directly to them having phones, my children apologized for complaining, and said they then saw the wisdom in us keeping phones from them at that time. We were surprised they made that connection and commented on it.
We don’t regret the decision.