It's pretty easy to attach your phone to a traditional tripod, but if you want a boom-style mount to film something on your desk or the ground, this DIY mount is a great option.
Instructables user hyperfocused72 shares how he made this impressive contraption. You'll need some dowel rods, a hose clamp, some lumber for a base, and a few other odds and ends to put it together. The walkthrough is pretty involved, but the resulting boom would be great for filming DIY videos at your desk, or for turning your phone into a document scanner. If your needs are somewhat simpler, you could also check out a tutorial on mounting your smartphone to a traditional tripod.
How to Make a Cell Phone / iPhone Camera Boom and Tripod [Instructables]