Using a phone as a bike computer?

I ride with a mobile on me as an emergency backup and re record gps data to log my rides (I don’t race, just like to track myself). I generally use my old Samsung S3 in a freezer bag for waterproofing. I’ve now been looking at bike computers like Garmin’s Edge Touring model with turn by turn navigation, think this would be handy to go find new routes, particularly on 50-100 mile rides. I’ve been thinking, why not combine the two? Less weight, less complexity etc etc. There are a few waterproof android phones about, some of them nice and small and some ruggedised so could be attached to the bar/stem in place of a bike computer, with one of the various apps providing bike computer duties, strava recording the ride in the background and Copilot or google maps providing directions. Was thinking about the Jeep Z6+ phone;

http://www.gearbest.com/cell-phones/pp_197181.html?currency=GBP&gclid=CNutndGxhcgCFUe3Gwod1usCKg

This seems to be waterproof, has GPS, it’s ruggedised which may save it in a prang, has dual sim slots so I can use two PAYG sims to have the best chance of actually getting network in the event that I ever have to phone for a taxi/wife, and being a little 4 inch screen would fit nicely strapped over my stem.

Problem is how to mount it to the bar/stem – no mount for this phone seems to exist, nor others particularly. Looks like there are various bar to phone mounts designed for motorbikes I could use however. The back plate appears to be screwed on to the device so I’m thinking I might epoxy a mounting plate to the back which I could then cable-tie to the stem.

Anyone done this or found any useful workarounds?