Give students an opportunity to familiarize themselves with phone settings. Allow them to assist one another and engage in the process of setting limits.
Discussion opportunities could highlight the need for phone users to check their phones only when THEY decide that it is appropriate and timely for them to do so. With the exception of important family alerts, the phone should not be permitted to interrupt a persons attention.
A second consideration may be what constitutes a "reasonable" limit for downtime. Experts regularly suggest no more than 2 hours of daily screentime for teens. One method of guiding this discussion is to start with the time a student wakes up in the morning. Then block off 9 hours of recommended sleep time in order to decide what time the phone should shut off at night. Then block out time for required activities (sports, chores, homework, dinner, exercise, shower etc.) and whatever is left over may be allowed for screentime.
Unregulated and discretionary use of screentime will become compulsive, habitual and disruptive to other activites.