BlackBerry did that , sort of, years ago. Just before the Storm if memory serves. I think it was ahead of its time style wise, the public was not ready for a flip smartphone.Would be sweet to have something about phone sized with a screen on it that you could literally use as a phone, then unfold it in fours as jkaod says and have a tablet-sized screen.
Casio did a phone where it was a flip phone but the screen twisted to be a full size screen when closed, open and twist to have the same screen but also a keyboard. My wife used one for about 5 years until finally updating to an iPhone last year.