The current trend in smartphones is the addition of a flexible display and movable sections, as evidenced by models from Samsung like the Fold and another rumored device. While producing a smartphone in the first place is a massive feat of engineering in the first place, creating one where the entire unit can fold is a much harder prospect, due to the display.
Even in instances where a smartphone includes a flexible display, there are limits to how far you can bend a material before it creases like paper. For displays especially, creases can make the screen appear unsightly with extra bumped sections, while creasing can fatigue the display and make it crack or break over time.
