I don't have an iphone. I have an Android phone which is larger (65mm width) than an iphone 5, but decidedly smaller than a phablet.

My phone is just on the edge of one-hand usability (I can mostly manage it but sometimes things get pretty awkward) and I often wish I had something iphone-sized instead, but choice is pretty limited among smaller Android phones (they exist, but tend to be old/slow/etc).

People I know with phablets use them like tablets (almost always with two hands etc). That's fine if you want a small tablet, but it isn't really an adequate replacement for a traditional smartphone. They're just different things.