I tried it breifly. Its definitelty doable, but I’m not much of a bodger. I tried my old Galaxy s2 in a timbuk2 mp3 pouch on a HR strap, worked to a point but I wouldn’t have trusted out on the trail.
I was looking the other day at smartphone tripod adaptors, a 7dayshop chest mount (or gopro one and adapter) and a decent case, but when you add it all up you’re knocking on £60-70 when you can get a chinese cam off ebay for £50, seems a bit pointless. There’s bar mounts cheap enough on ebay, but handle bar footage normally looks crap, decent last resort I suppose.