Review on Self-Buddy HYDRO - Smartphone Holder for Fitness Water Bottle - Workout & Running Sleeve - Water Bottle Phone Storage Solution by Jack Bhowmik

It's a little pricey but I've found it useful for everything from taking photos in a public place, clipped to a railing or pole, to to wrapping around the base of my Nutribullet to watch videos while I cook or wash dishes. There are definitely many other options, but having a magnet on my case made it a lot easier to use these mounts in whatever situation I needed. It fits my standard Yeti cup and the cup hand ensures it fits very snugly and doesn't slip off (because Yeti style cups are tapered).