In November 2017 KGI Securities analyst Ming-Chi Kuo estimated that Apple will launch three new iPhone models in 2018 - two of these will sport OLED displays, the 5.8" and 6.5" models. A new report from Digitimes, however, says that Apple may eventually only launch the larger (6.5-inch) OLED variant in 2018.
According to Digitimes, Apple is developing four new iPhones: two LCD Models (5.8" and 6") and two OLED Models (6" and 6.5"), but it may abandon the smaller OLED variant. This is mostly due to lower than expected iPhone X sales.
Samsung is currently providing the OLED displays for the iPhone X, and it is of course highly likely that SDC will also supply the OLEDs for Apple's 2018 lineup. There were some reports that LG Display was selected to supply the 6.5" OLED for the large iPhone 2018 model - which is possible because Apple is said to expect to sell around 15 million such phones in 2018 and LGD will have enough capacity.
Samsung is likely to be Apple's OLED supplier for the mass volume 5.8" OLED variant (some estimate SDC's OLED shipments to Apple in 2018 to be 180-200 million units). But if Apple cancels the smaller OLED, it may leave SDC with no Apple supply agreement for the 2018 iPhones, which may be what's behind the company's recent reported decision to delay its A5 flexible OLED production fab.
This is of course just a rumor at this stage by Digitimes. ETNews for example posted an article that confirms the 5.8" OLED 2018 iPhone model, quoting "industry supply chain" as the source.