I think my full-blown mobile rotary phone is EVEN cooler:

https://www.stavros.io/posts/irotary-saga/

It actually makes calls itself and has a SIM.

ok you win

Someone should make a Bluetooth box that outputs to a standard phone connector so any standard phone would work. Has anyone done that?

Someone does - the Cell2Jack is only $36 USD:

https://www.cell2jack.com/

I use one with a 1970's vintage rotary desk phone and it works well.

I think I've seen it, I was thinking of making a USB one. I might!