While I believe that is technically illegal in many jurisdictions, I agree a quick peek is fine.

What I routinely see, though, is folks with their heads solidly down and noses buried in their phone. Just in the past week I've seen two folks _watching video_ on their phones while I was bike commuting. This is terrifying.

And sure, not everyone peeking at their phones at full stops will also be looking while they're moving. But folks who look at their phones while moving will definitely be looking at full stops, too.