Why foldable iPhone? Apple, bring back iPhone mini.
The fPhone might just be the Mini replacement...if you look at the rumored specs it's not really too different in size from my 13 Mini. The two sides add up to a bit more than the Mini's thickness, so if it folds flat that will be about the same (and mine is in a case so it would effectively be smaller for me), the folded screen size is pretty close, and the only time I've seen a weight mentioned it was roughly the same too.
So, if you use the fPhone folded, it's going to feel pretty close to a Mini, theoretically. But, for once the smallest phone will have the top specs (except for the camera), and will be the flagship. It's going to be more expensive obviously, that goes with being the flagship, but it will mean we can have the advantage of a small iPhone for one handed usage but then be able to open it up for appropriate uses.
I worry about what's going to happen if my Mini has an issue...it's hanging in there so far and I have it wrapped in protection (I've had more screen protectors break with this phone too, thanks to raising a toddler), and the battery is ok for now. It's a 4 1/2 year old phone though, eventually it's going to have to go...I'm about where I was with my iPhone 5, I had to go up to the X and was not at all happy with the size of it. I don't see Apple making another Mini anytime soon, though if they were smart they would bring one out every 4-5 years to keep the few percent who buy them happy, because most of us want to stick with a smaller phone and resist upgrading to a bigger one (even when the prices is the same). Maybe someone at Apple will finally get it, or maybe all of us Mini users will grab a fPhone when it shows up because it works and will be top spec for a change. I guess we'll see sometime this year.