Some company made one once, back in the early 2010s. I think they released a successor the following year, but neither phone sold well enough to keep going. It would be cool as hell if that were more common, though.
At the time they've been seen as a gimick, mostly because they were PRed by the government as our local invention and an iphone-killer it wasn't. That's a shame.
There’s nothing technically stopping you from building an android smartphone just the way you like. In fact, there’s extreme modding folks that do things like already. What we really lack is a future-proofed connector standard for component connectivity that just works.
I know it's not the exact same, but most folding phones are double sided screens on one face. I just don't know how much I'd use it if it was a non-folding style with front and back screens.