I'm baffled that Microsoft still didn't even attempt to make the Courier. Its not like anyone else really seriously tried it (well I guess Lenovo - ? - had that weird tablet thing with dual screens), and it would make a great Surface product.
For me though for this foldable into a phone device, I would want it to have 2-3 creases, so that we'd get 3-4 sections, where we'd get a bigger like widescreen tablet size when full unfolded, but then a more compact phone shaped thing. If you do 4 folds, you could get multiple, where it could get to phone size, then you could square it off so it'd be more book shaped/sized, then fully unfold it into tablet size.