Yeah they're ready-to-go touchscreen interfaces/displays that can be implemented in tons of ways. I've been thinking about setting up my old Note 4 as a touch screen interface for my 3D printer, and old tablets as wall mounted interfaces for Home Assistant, which are just two possibilities.
I was poking fun at the seeming desire for a physically tethered phone as to power a device without a battery, it would need to be plugged in.
But also, you may have missed the likes of ELKeyko Wireless Phone 2021 The 4G LTE Android 10 Fixed Wireless/Cordless Desktop Phone with VoLTE, WIFI,BT and WIFI HOTSPOT Smart Phone Cordless landline https://amzn.eu/d/ffotKoV