$1 Super Simple Smartphone/iPhone Tripod Mount

Could not be easier.

Dollar Tree sells these for, guess what, a buck. This particular model has a head which attaches with a 1/4-20 thread bolt just like any tripod mount. Just unscrew the head but hold onto the stick.

Just screw it down. For an added bonus, plug the small cord into your headphone jack for a remote shutter release. Assembled, the collapsed selfie stick even makes a serviceable handheld.