I'm not sure if the 2013 comment is true or not but I think it's in relation to this (from the article):

>For the past few years, parents, researchers, and the news media have paid closer attention to the relationship between teenagers’ phone use and their mental health. Researchers such as Jonathan Haidt and Jean Twenge have shown that various measures of student well-being began a sharp decline around 2012 throughout the West, just as smartphones and social media emerged as the attentional centerpiece of teenage life. Some have even suggested that smartphone use is so corrosive, it’s systematically reducing student achievement.

But of course it was already dropping quite consistently at that point. Perhaps smartphones made it worse, but clearly, concluding that they caused it seems very far fetched.

I went to school in South Korea, it's basically illegal to ban smartphones in schools, but even now, top high schools ban smartphones. parents prefer it, and students get good grades. But I'm not sure about the causality