The problem here is the why. Why would someone want to convert a product into another product category and in so doing, that product with a primary purpose of in this case a smartphone becomes compromised. The same thing applies to laptops converting to tablets, or cars converting to planes, or watches converting to helicopters, etc. Primary purpose becomes compromised.
People use smartphones because they are portable and they have defined use cases. That is a fundamental aspect of why people use them. A smartphone is resilient in its form factor like a desktop is. In the case of a smartphone, the screen, the 'computer', and the input modality is wrapped up into one device that can be held and used with just one hand. With desktops, an over 50 year old technology, the mouse and bitmap screen are resilient where the input mode is precise down to 1 pixel and the screens can be much larger and compute power significantly more. Each have their use cases.
People using smartphones on planes, trains, buses, waiting in line somewhere, plugging into their car for Carplay, sitting on the couch watching a movie and surfing the web, etc. As soon as something like a foldable smartphone unfolds, it changes into a tablet. And a tablet can't reliably be used with one hand, and it takes significantly more effort for a User to input into it, as the arms and hands have to travel farther to hit targets on screen. This reality is aside from the many compromises a foldout tablet would be like.
The point is that there are categories of products for a reason. The right tool for the job. The central point I'm making is that dedicated devices like smartphones and tablets won't be replaced by foldable smartphones and foldable smartphones will end up being niche.