What skills do you think, specifically, kids will be robbed of if they don't have access to a smartphone?
Learning how to interact with the internet. Basics for caring for valuable objects. Learning how to be mindful about your relationship with technology.
But i think it's more about just being socially equal to those around you, as others have mentioned, and the ability to think like other kids who have smartphones too. Thats important, in many, many ways.