If every year, we are offered a bigger iPhone than before, who can imagine what the future mobile phone looks like?
Except Apple hasn't gotten larger every year.
There was the original 3.5" screen from the iPhone to the iPhone 4S. The "tall" 4" screen from the iPhone 5 to the iPhone SE (same width as the original screen, slightly taller.) Then introduced simultaneously were the "large" and "plus" screens - iPhone 6, 6S, 7, and 8 at 4.7" and iPhone 6 Plus, 6S Plus, 7 Plus, and 8 Plus at 5.5".
That makes in the "main line", four phone
screen sizes. 3.5" was replaced by 4", then 4.7" and 5.5" were
added. Every 4.7" screen phone so far has had identical phone body sizes. Every 5.5" screen phone has had identical phone body sizes. (To the point that you can put an iPhone 8 in a case made for an iPhone 6, possibly with modification to make the camera fit. I have my iPhone 7 in a case I originally bought for an iPhone 6.) All the 4" phones are basically the same size - while the physical shape of the iPhone 5C makes its cases not fit properly for the 5, 5S, and SE, they do fit. They are all basically the same size.
And the 3.5" phones got
SMALLER over time. The iPhone 4 and 4S are quite a bit smaller than the original iPhone and the iPhone 3G/3GS.
That leaves the "oddball" phone - the iPhone X. It has the largest screen yet - 5.8". But the body of the phone is noticably smaller than the iPhone 6 Plus - iPhone 8 Plus. It is in fact *MUCH* closer in size to the iPhone 6 - iPhone 8. 5mm taller, 3mm wider, half a millimeter thicker. So while the *screen* has gotten bigger than the previous generations, the *phone* itself hasn't.
And that's the current trend in phones. They got physically bigger for a while, then the bodies started to shrink while the screens took a larger portion of the face. The "truly big" phones (6" screens or bigger - up to an infamous 7" Samsung Galaxy W from 2014) have largely disappeared, other than a real niche market. Even Samsung's "giant" current phone, the Note 8, has a 6.3" screen, but the body is no bigger than previous generation Note systems, because the screen takes up most of the face, rather than having a large border like in older phones.
I honestly think that the Note will remain the largest mobile phone. We'll see phones'
screen size increase until they fill the entirety of the face of a body the size of the iPhone "Plus" models, and that will be the largest phones. The reason phones got bigger was to hold bigger screens. And the market showed multiple years ago that bodies that held 6" screens were as big as people were willing to buy. So no, we won't see iPad Mini sized phones. They tried to make them, nobody wanted them.