It depends on the situation really. hated downtime at my old job because they were strict, if there was nothing to do they would make us do something menial like wipe the counters in a circle over and over until there was something to do, we couldn’t go on our phones. At my current job, I’m on my phone during downtime right now so it’s not as bad, though i still have to do the duck and cover if I see my boss coming around since technically at this one we aren’t supposed to do this either.