Where do you put your phone while you're riding your motorcycle? There are, generally speaking, three very common places. One is a mount on your handlebars, assuming you feel good about the vibration-damping capabilities of your phone mount. Another is a pocket somewhere in your clothing. And the third place is anywhere else that isn't the first two places.
Me, I generally don't feel good about putting it in one of my pockets. I like to have it with me when I'm riding, either because I want to listen to music, or I might want to take photos while I'm out, or in a worst-case scenario, I might need to call someone if something goes wrong. But I usually don't keep it in a pocket. Instead, I'll keep it in a bag, or in a storage compartment, or sometimes in a mount on the handlebars.
Why don't I like to put it in my pocket? Usually, it's because I'm concerned about what might happen if I crash. What if I want to use my phone to call someone in an emergency, but it's so broken that I can't? What if the phone actually serves to injure me more because it was on my person when I crashed?