The difference in screen size between tablets and phones is much less apparent now than it was 2 or 3 years ago.
Yay?
Try getting out of the iPhone bubble for a while - you'll find that in the real world, phablets are not just something that you make fun of.
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.
E.g., I see huge numbers of people standing on the train using their phone with one hand (while hanging onto a strap with the other) or walking down the street, using their phone with one hand (while carrying a bag with the other), etc.
She's already used to having to charge her phone every night, because while her old phone might've lasted 2-3 days it was easier just charging it every night.
She holds it two-handed, portrait, to text and interact with facebook, and did with a smaller phone too because she can type much faster that way.
She's comfortable reading on it.
It fits in her pockets fine.
I prefer my Nexus 4 + Nexus 7 as an approach, but for a bunch of people, yes, yay.
That said, I don't want a 6" phone. My Nexus 5 is too big. Just a bit smaller, and I'd be able to use it comfortably one-handed. I'd go 4" over 5" if there was an option with the price and performance I want, though 4.3" or 4.5" is probably perfect for me.
I have medium-small hands, and the Nexus 5 is hard to use one-handed. I made a case for it out of carbon fiber, and that improved things slightly by adding a bezel that sticks out from the screen by 1 mm or so. Its height is also at the upper end of what I want in my pockets. Unfortunately, the iPhone 5S is the only current/recent high-spec smartphone I know of that's the size I want, and I don't like iOS. When is Sony going to offer the Z1f outside Japan?