I work as a security guard and my job has a no cell phone rule. I work at a pretty remote location and I get up and do a patrol every 2 hours. There is not much else to do during downtime at my work between doing rounds. I never talk to anyone only the utility workers when I make lunch or the person I am relieving or my relief when they come to see me. But I tend to ignore that rule anyway. I use my phone to watch movies, YouTube, Reddit, or just other time killing even bringing my Switch. I never see my supervisor only once a week or every other week. So to me a rule like that is just incredibly pointless to have.
Man I wish I could work from home where I don't have to worry about looking busy all the time.