Sounds pretty serious. Why not take a moment and ask them what they are doing and why their phones help them out, rather than projecting your worst expectations onto them en masse? It'd be much easier to help them out that way, if you are really interested in assisting via your personal values.

Otherwise it appears indistinguishable from shaming them inwardly, which could be even worse than doing it loudly, in person, and giving them a chance to defend themselves.