Not cheap but I really love my RAM X-grips and mounts. They're primarily designed for motorcycle use so they genuinely hold my phone with no fears of it falling off. It's a whole system and you mostly buy pieces a la carte but this mount plus the phone grip and then a stem to connect them. If you look around you may or may not be able to find sets that have two or three of those pieces in them for a lower price.

It is, as I say, not cheap, but it's much less expensive than trying to replace your iphone.