This is a product category that kind of exists. There are companies like https://nexdock.com https://nexdock.com making these "lapdocks" that work with phones,

This is a product category that kind of exists. There are companies like https://nexdock.com https://nexdock.com making these "lapdocks" that work with phones, but also with things like Raspberry Pis. And then there are dozens of Chinese clones on AliExpress. I'm personally using DeX (Samsung's desktop mode) on daily basis. It is a bit clunky, but better than owning, maintaining, and carrying a second big device. The "real computer" on my desk has only work stuff on it, and all my open source development etc. happens in DeX, mainly via the Termux app.