I take my phone to spinning, and place it upside down next to my bike (so the light doesn't disturb anyone. Our spinning studio uses blackout shades and you spin in the dark). My phone is connected to a Bluetooth HR strap I wear. Probably not necessary, but I'm a data geek. I don't look at it during the class, but look afterwards to see if my perceived work matched what the phone recorded. But I think you're likely right that people can't do without their phone for an hour so they want it nearby.

I have a trainer at home and a spin bike at work (we have a large room where we can exercise. We have organized yoga and pilates classes three times a week, and a spin bike. Maybe we'll get a treadmill eventually). I watch movies/music videos/sufferfest videos on my ipad I can strap on the stem on my bike on the trainer and can stap on the spin bike at work right below the handlebars (I only lose one hand position, and keep the other two) and it gets all sweaty. If I'm only listening to music I set my phone/ipad on a stand near the bikes.