Your smartphone already comes with a couple of decent cameras for selfies and videos. By attaching a lens to your phone, you can do more with it. Here are 2 adapters that let you attach Sony or Canon lenses to your smartphone:
ULANZI DOF Adapter with Sony E Mount: turns your smartphone into a real camera by allowing you to use your phone with a full-frame lens. They do recommend using a fast lens (f0.9-f2.8).
Beastgrip DOF Adapter MK2: lets you use your DSLR lenses with your smartphone. It is designed for full-frame lenses. It feature a Canon EF lens mount.
Have you found better adapters for attaching DSLR lenses to iPhone and Android phones? Please share them here.