Why do some see young people's increasing reliance on smartphones as a health crisis?

The increasing reliance of young people on smartphones is considered as health crisis for it causes addiction. The attention of mostly young people is on smartphones and that they cannot stand a day without using a phone. With this, it could affect mental health for it causes depression and anxiety to face other people.
Moreover, young people may also develop poor posture and text neck, a condition of stabbing pain and cramping after looking down at phone for too long.