If the class is watching a video and you need to have the closed captioning for the video turned on, watching the video on your phone may be an appropriate use for the phone. Your teacher should give you specific permission to do this.
but.. .
If you're just watching some goofy Youtube video, or a new Netflix show, instead of paying attention to what you need to do in class, you're wasting your time. You will probably miss critical instructions, important material or just basic directions while you are distracted.
Your teacher will probably be less patient with you than the students around you because you're showing with your actions that you believe the class is less important than a random video clip.
