I got the idea off a user forum for my Ninja 650R for how to mount a phone/gps.
I used three items to mount the phone to my bars:
Ram Mounts Short Double Socket Arm for 1" Ball Bases
Ram Mounts Universal X-Grip Cell Phone Holder with 1" Ball
Ram Mounts Motorcycle Handlebar Clamp Base with M8 Screws
It's seems to hold it tight and is very adjustable due to the double balls involved. It does not block any of my gauges and is low enough that even in a full tuck, I would not hit it. The tether is not big enough to go around my Moto X so if you have a phone over about 5 1/4", don't bother hooking the rubber tether up.
This is the most important piece because it holds the phone, so being tight is critical.
For this piece, check it's orientation before you tighten it down. It rotates about 25 degrees and may need to be adjusted for the right angle.
I am confident it will hold up.