Broadly speaking, a general purpose computer is one that can do anything (like an Apple IIe) and the opposite is one that is constrained to do a few specific things (like an ATM). Whether an iphone (or a wintel computer with UEFI, or an Android phone locked by the hardware manufacturer, or etc etc) qualifies is a matter of semantics, and not interesting to argue about; I elided this distinction because (I imagined) the kind of people posting here would be familiar with it and know what I meant.
A more nitpick-proof way to phrase my point would be that an iphone is a general purpose computer controlled by Apple, and it tries very hard to look like a general purpose computer controlled by the person that bought it. The customers want to have their cake and eat it too; they want the power of a general purpose computer, and the security of a locked-down appliance. You can't have both, but Apple's size and popularity is a testament to how close they have managed to get.
