"Using phones in classrooms can distract students from paying attention to and concentrating on lectures." because, 1. paying attention includes looking and listening, and 2. focusing and concentrating are basically the same :)

That looks like a great answer to me. You have pointed out the main reason for not having smartphones in lectures. A secondary point could be made that other students and the teacher are entitled to a certain level of privacy within the classroom environment and visual recording devices such as smartphones, compromise that privacy.