Phones can already be used as a webcam, e.g droidcam app. No need for special hardware.
It has great linux support and works great with OBS (and its chroma key filter)
I tried it with my phone and latencies made it unusable for video-conference usages. Given that this is my main usage reasonable low latenzies are for me much more important then super good image quality. So when I had to buy one recently I ended up with a ~70€ not super good but not bad webcam. I thing normally I might have bought something like a C920 but prices-return ratio was just madness when I bought (sight, Covid19 madness ;=) )