I looked at these a while ago, the cheap adapters from Amazon/eBay are just that – cheap. Out of 2 ordered, one broke, the other didn’t work that well (stuck on an old phone case). They are also about 30 day delivery for most of them
I ended up getting a custom 3D printed case from RaceWare. UK made, turned up in a few days, and so far (5 months use) a really good investment (yep, much higher price than the stick on adapters). I leave my phone in that case all the time, the mount is quite slim so doesn’t impact sticking the phone in jeans pockets.
Mine is built to hold the phone in landscape mode as portait wouldn’t work for Sufferfest videos.
The adapter on 76 Projects didn’t come up in my search, I’d have tried that one first if it did.