Are cell phones a distraction in class?

To prove a point, a math teacher asked her class to put their phones on the corner of their desks, and every time they received a text or a notification - to mark it on the board.
THIS is what the board looked like after just 30 minutes.
23 students...
58 texts
182 social media notifications
28 other notifications
That's 268 disruptions in a half an hour.
The teacher wrote, "Parents PLEASE find a way to block students' access to these disruptions during the school day"