I also had Problems to fit a Samsung S6 in the Adapter.
Seccond Problem is that my hardware store didn't sell the metal parts from your list.
I used stronger springs. This caused problems whit durability.
Would you put in the construction files from openscad? So i would be able to adapt your construction to my demands.
I also had designed a small part which fits between the clamps so you can use a wing nut without breaking the parts if you tighten the nut.