MG Siegler, on the iPad and phone sizes…10 years ago:
It’s a different type of computing device. You can argue that as phones get bigger, they veer too close to tablets for a tablet purchase to still be justified. But I do believe we’ll see phone sizes eventually settle in the 4 to 5-inch range, while tablets go the other way: larger, as they embrace their destiny.
That’s not turned out to be the case; people still love big phones. (I have a Max.) None of Apple’s scurrent line save for the SE fit those dimensions.
But the larger point is correct in a couple of ways. First, the iPad and the phone are different devices. Second, and closely related: you could have an iPhone and not an iPad, but not the other way around.