There are two uses for flexible screens in folding phones – one is to turn large phones into small tablets, and the other is to turn small phones into large phones.
It is the later application that ZTE is pursuing in their Global Design Database published by WIPO (World Intellectual Property Office) on 5 March 2019.
That shows a device with a clamshell design which folds open into a normal-sized smartphone.
Noticed by LetsGoDigital, the device has some unusual elements, such as that the second folding half does not cover the bottom screen fully, allowing a portion to remain exposed, presumably for caller ID functions.
The other is that the hinge assembly intrudes somewhat onto the screen surface.
See it rendered more prettily below:
It is not known if ZTE is planning to bring the device to market, but readers would recall that ZTE was first to the market with a modern dual-screen smartphone, the now forgotten ZTE Axon M, so the company may be ready to surprise again sooner than we think.