I wanted such a thing for a while, but didn't see it in shops. But when I bought car holder it occured, that construction with two plastics claws covered with rubber can hold phone very good if you press them 3-4 clicks more.
After that I've bought second holder made by onext (this was the first model offered in a shop). It suits good by it's size and claws beside rubber have projections on their side, which prevent phone from leaping out. Disassembly was accompanied with cracking and flying springs. As far as handlebars stem on my bike is square it was sufficient to press the holder to it. I've made four pairs of holes in holder and attached it with strainers to the stem.
My experience shows, that phone is beeng hold firmly, it doesn't move even while speed ride through the forest with jumping on roots and pits.
. Next target: speedometer and voice navigation in navit.