Can't ride with a cell phone in any of my jeans pockets, I have no shirts with pockets (and would use that anyway in case it bounces out), and I refuse to wear a jacket with pockets when it's a heat index of 101 and humidity is 78%, lol.
I had actually briefly had the thought of using an armband for my phone and having the trainer just call me and talk to me through that while I wear earbuds. She pointed out a major flaw in my logic: There's zero cell reception anywhere inside the barn. No phone calls, no text messages, no data, etc.
The wind of heaven is that which blows between a horse's ears. ~Arabian Proverb