The idea for this phone holder came to mind when I was looking for something to hold up my phone while on my bed since I dont have a nightstand. I realized I could design the joints and arm in a way that can be used for multiple purposes. The fun thing about this phone holder is that you can get pretty creative in the way you build it, like a puzzle. For many, the downside of this design is that it has to be screwed in to the table or wood frame in order to achieve the most stability, unless you find another way to attach it firmly without using screws and creating holes. From my personal experience, two length arms works best and is very stable. When you add a third arm thats when the entire thing becomes weaker and more wobbly, it all depends on the moment exerted by the arm and how you balance it. 

In order to build the arm you will need a small amount of super glue to glue to small parts together, one at the base and the other at the phone holder. The phone holder will also require one rubber band and I would suggest to add more rubber bands at the fingers of the holder for better grip. Besides that, everything else doesn't require anything but your creativity and a good find of use. The pictures show a couple of configurations you can use but are not limited.