Here is a flexible smartphone holder that makes it easier to exercise with your phone while running on a treadmill or riding a spin bike. The iTODOS Flexible Cell Phone Holder has an adjustable gooseneck. It has a 17.7″ long arm. It works with smartphones up to 4.3″, including iPhone 12 and Samsung smartphones.
This smartphone holder has a 1/4″ interface that supports various cameras. You can find out more about it here.