A pocket or in the waistband of my pants, wearing a belt will help it stay better!
However, you carry it, make sure it is on your BODY so if there is a mishap you can call for help!
Vest pocket. Or you can get a leg hoslter that's designed for holding a phone while riding.
I know there are belts that can hold things like your phone. My trainer also had something like an arm holder but it goes on your leg instead so it’s not in the way. If you were going on a trail ride you may want to invest in a saddle pad with a pocket for your phone and belongings that way you don’t have to carry it- this may not be a great idea for your everyday riding though.
Hello Katie, I keep it in my jacket (I often wear a sleeveless jacket ) 🙂