Apple is expected to launch three new iPhone X successors this September and apparently, the company is referring to them as 'S' devices as they are externally similar to the iPhone X and only sport internal upgrades. The largest iPhone of the bunch will be a 6.5-inch model internally referred to as 'D33'. The 'D32' is the upgrade to the current 5.8-inch iPhone X while 'N84' will be the cheapest of the lot and will sport a 6.1-inch LCD screen and come in multiple color options.
https://www.notebookcheck.net/Upcoming-iPhone-X-successors-will-offer-diverse-choices-but-Apple-hasn-t-zeroed-in-on-the-names-yet.325658.0.html