Mileage may vary.
In Asia, the oversized phones have been big as they either haven't had a corresponding use for tablets or not had the same disposable income to have both; the 'Phablet' has served both purposes in a compromised but affordable way.
I am a guy, so have my phone in my pocket; the 6+ is just too freakin' huge. I currently have an iPhone 5 and will stay on it for at least another year as I got it just after the 5s got out. It is a great size as a phone, the 6 is a good size as well and I can see me using it, but there is no compelling reason to upgrade just yet.
When I'm out, apart from a phone, I use the Podcast app extensively, as well as maps. It can get cramped for typing in Facebook or iMessage, but the Retina screen means it is not too small to read from.
I also have an iPad 4 which I use a lot at home, and my wife has a Retina Mini, which she is addicted to; I use my iPad 4 for a lot of web browsing and running a few apps like a TV Guide app (OzTV), Facebook, Snapseed, Phonto, Instagram (unfortunately they only have a phone app, but the larger keys are useful), and a few other things. I can't be bothered with games, not my thing, though it is good for that.
My wife is an avid Social Media user, web browsing, Pinterest, Facebook, Instagram, Snapseed (for Instagram pics), takes photos of her crochet with the iPad (which turn out better than most similar pics on Instagram), and she also plays a lot of social games for relaxing. The Mini is the perfect size for her and goes absolutely everywhere with her; it fits nicely into her bag. My iPad is too large and heavy for her use, but is a perfect size for me. Either the iPhone 5 or 6 is the best size for me in a phone.
If they ever do put out a 13" iPad Pro, if it had inbuilt stylus support, then that would have a usage case for me with my drawing, a niche currently only the Surface Pro and Galaxy Pro serve in the Aus$1000+ range. Paradoxically, by far the best mobile drawing and painting apps are on the iPad, despite its lack of stylus support, a niche just waiting to be exploited.
Various sizes have their ideal usage, which may vary with different people, but "Phablets" to me are compromised make-do devices, too big for a phone, and too small for a tablet, which makes more sense for women with their bottomless handbags than for guys and their jeans pockets. Just my take on it.