Students will not use cell phones during class unless directed to do so by the teacher.
Studies show that cell phones can distract individuals, even when they are not using the phones. People who have their phones nearby are often distracted and perform more poorly, even with notifications and ringers turned off. There is also a phenomenon developing known as nomophobia (fear of being away from a phone).
I see it firsthand year after year. Students who have cell phones out during class, even on desks face down, struggle with listening and following directions, and they often do not perform as well as their peers.
An article I read asserts, "The reason is that smartphones occupy in our lives what's called a "privileged attentional space" similar to the sound of our own names. (Imagine how distracted you'd be if someone within earshot is talking about you and referring to you by name - that's what smartphones do to our attention.)" (Elgan).
We still have much to learn about how smartphones affect us at school and in the workplace. However, I am standing firm in that students will detach from phones for the period.
The following are three short articles from various sources that support my opinion: