I feel it's unfair to be blaming phones, social media, and multiplayer video games for being the way teens get some peer socialization in a world that is so deeply unfriendly to teens having independence.
danah boyd spent a bunch of time studying teen use of earlier social media, and then for personal reasons moved on to help run teen crisis text hotline.
Her thought for why US teens are struggling are the lack of non-parent trusted adults in their lives.