Yes, but there's a huge degree of bias whenever you ask people anything. Obviously teachers are going to think phones are detrimental to class focus, and thus they're more likely to say their ban helped with that same focus

Same thing If you asked students, but reversed

Sure, I just don't trust results from subjective studies, unless it's tracking trends over time. So maybe if they had opinion polls like this before smartphones were a thing in classrooms, while smartphones were a thing, and after they were banned I'd trust the results somewhat. But if we're just tracking an after-the-fact poll, it just feels like confirmation bias. I believe teachers have an incentive to overstate the impact of policies that give them more control, because they want to encourage more such policies, even if they aren't effective at achieving tangible results.

So yeah, I distrust this type of study. I don't think it's necessarily worthless, I just don't think many conclusions can be taken from it.