OnePlus has patented a foldable smartphone with three displays that all link together. The Tri-Fold Foldable Device could relate to the 'Flex In & Out', which Samsung Display exhibited earlier this year.
https://www.notebookcheck.net/OnePlus-patents-a-Tri-Fold-Foldable-Device-with-an-ultra-wide-display.580765.0.html