So you want to use your smartphone to capture better quality video and audio? iKlip A/V might help. It is a smartphone mount that lets you pair your smartphone with an external microphone to capture better quality audio. You get an integrated microphone preamp with phantom power for XLR microphones.
The iKlip A/V has a expandable smartphone holding bracket, an ergonomic handle, an activity LED, and a headphone port. It should work with most smartphones from 3.5″ to 6″. You can power it with 2 x AA batteries. More information is available here.[H/T]