Meet the Ztylus GoMount: a GoPro mount that lets you attach your favorite GoPro camera to your phone. You are going to need a Ztylus case to get started. Using the GoPro app, you will be able to get a live preview on your phone. The mount rotates 90 degrees, so you can use your phone in portrait or landscape mode.
The mount has a flexible arm, so you can change angles and get the best shots possible. Costs under $45 at this time.