A lot of older PC games can run just fine on modern phone hardware. I’d buy a SteamOS version of a phone that has some modular or built-in set of buttons and analog sticks. I don’t know how the app ecosystem would work for sensitive things like banking but it’s mostly a minor issue for me.
I wouldn’t buy it to replace my phone. I want to keep that and my gaming devices separate.
I would buy it a dedicated handheld in a similar form factor to a phone + some controls. I’ve actually been looking at the AYN Thor for this exact use case. It would have to be the right price too.