One has to imagine that if you work at Apple, your boss isn't going to scold you for looking at your iPhone. Who shoots you a dirty look in a meeting when your cell rings at the Verizon offices? If I worked at a company that made cell phones or provided cell service, I would spend at least two hours of my life trying to figure out how my company financially benefits from me — personally — answering a call or sending a text.
But seriously: It is kind of rude to leave your cell phone ringer on at the office. This can't be surprising to you. If it is, you might not realize that most people have learned to put their phone on vibrate in social or public situations and are content to simply obsessively check it surreptitiously, 14 times a minute. And guess what? That's cool. Do that. Find ways to check your phone when no one's looking, and we're all happy.
But what you can't do is assume that everyone wants to hear your Ed Sheeran ringtone when they're in the middle of crunching numbers on their Excel spreadsheet. (You also can't assume anyone wants to hear your Ed Sheeran ringtone at all, crazy as it may sound to you, Ed Sheeran Number One Superfan.) You also can't bring your cellphone to a meeting and leave your ringer on. That's crazy. Everyone knows the point of meetings is to pretend to listen to people while you actually space out. Leaving your ringer on acknowledges there are a lot more important things you're just itching to attend to. Don't ever let your colleagues know that.
Now, let's give the standard caveats. Your kid is sick. You're waiting to hear if you need to pick up your car from the garage. There are reasons people might need to leave their phone on. But all you have to do is give a quick heads up to those around you, and ask if it's cool to duck out for the call. Remember, a little courtesy goes a long way.