For 2018, we're expecting to see more design evolution with 6.1-inch and 6.5-inch models blanketing the bottom and top of the iPhone X respectively. Benjamin Geskin, who has a reputation of leaking Apple news ahead of schedule, has come into possession of dummy units of both the 6.1-inch iPhone and the 6.5-inch iPhone X Plus (we don't know if this will be official name, but that's what we're going call it for now).
If you're familiar with the design language of the iPhone X, nothing should be too surprising here. The 6.1-inch iPhone has a display notch up front, but its back is more reminiscent of the iPhone 8 thanks to its single camera. The iPhone X Plus, however, simply looks like a supersized version of the current 5.8-inch iPhone X.
When placed side-by-side, you can see the slight size differences between the two handsets, although we wish that a current-generation iPhone X was thrown in for good measure. While these dummy units are by no means "official" Apple hardware, they are likely constructed using official CADs, which makes their appearance likely very close to what we'll see in September.
All three of the new 2018 iPhones (which will include an upgrade to the existing iPhone X) will feature Face ID along with Apple A12 processors (likely produced using a 7nm process). The 6.1-inch iPhone, however, will be the odd man out with a more traditional LCD display instead of the more expensive OLED panels that will be used on its smaller and larger brethren. The use of an LCD panel also means that this will be the cheapest of the three new phones.