A used think pad is so cheap, cellphone to laptop conversions are generally not worth it.
However; this is the keyboard you want for a phone.
You can get a portable USB C display for luke 75$ too.
Discussion
Interesting, I am putting a premium on portability - but the touchpad is a nice feature.
Have you used this in the past?
Yes I own it. It folds up nicely. Folds out to full size. Excellent battery life. Usb C port for charging. It has three buttons to switch devices easily.
You can pair it with up to 3 devices at once.
To repair just hold one of those buttons to assign a device.
The track pad is fine if needed. I usually carry an extra wireless mouse.
I use it when I connect my phone to TV and when I work in coffee shops.