A 1/4" hole was drilled approximately 1" from each end and centered.
The ends were rounded on the disc sander.
Two bases were made, one for the phone and the other for attaching to the tripod. I cut a 1-1/8" wide dado across each base and drilled two holes.
From the extra 1-1/8" wide strip I cut four pieces around 2" long, drilled and rounded one end, then glued them into the dado. A screw through the bottom helps hold them in place.
The tripod attachment base got four 5/16" holes. I probably won't ever use the extra holes but they are there if I should want them.
The walnut tripod has a 5/16" threaded rod sticking out the top, the base slides over this and is temporarily secured with a wing nut.
The arm joints are linked with 4-1/2", 1/4x20 carriage bolts.
I made a phone mock up from MDF for testing the mount. A rubber band secures it in place.
The walnut tripod has adjustments for height and angle.
Jan 2017 Update: I still use this arm but have since mounted it to the wall to save floor space. Dimensions are between pivot holes.