I temporarily need a quick smartphone camera holder today and my first thought is to grab a hand sized four by four to slice a kerf just deep enough to hold the phone (with casing) but not too deep so as to interfere with the lens.
I only have a chop saw to shape the wood but I do have lots of scrap wood laying around to experiment with.
Have you ever made your own smartphone camera holder out of a block of wood? What did you find works best (for quick results today)?