As a person from the developing world I feel obligated to say that I find your assurance quite unconvincing: the negative effects of smartphone at this point in time is invariant globally, and whether they are a net positive or negative is at least debatable.

And in relation to your first comment, most sane people would agree that "tools" don't exist in isolation - neither come into existence out of nowhere.

This reductionist position of treating extremely complex machines with deep social interactions as a tool like any other is objectively wrong, and I believe the reasons are highly obvious but I can expand on this if you disagree.