It is well documented since before the smartphone age that adolescence comes with changes to circadian rhythm (e.g., [0]) which makes teens want to stay up late

It is well documented since before the smartphone age that adolescence comes with changes to circadian rhythm (e.g., [0]) which makes teens want to stay up late at night. It is certainly stronger evidence than personal anecdotes about "teens are always on their phones". [0] https://pubmed.ncbi.nlm.nih.gov/19546564/ https://pubmed.ncbi.nlm.nih.gov/19546564/