There is a large and growing body of evidence indicating that pervasive phone connectivity has led to large increases in psychiatric issues among all demographics, and particularly among younger people who have now grown up immersed in a phone culture.

More informally, smartphone usage by children promotes a short attention span, a lack of any sense of presence where actually situated in the physical world, as well as less and lower quality interaction with others, leading to poor social skills, anxiety, social isolation, and a focus on superficial social signaling over meaningful human interactions, ultimately producing the mental illnesses referenced above.

See e.g. https://kagi.com/search?q=summary+of+mental+health+outcomes+... -- there are far too many sources to even list here.