No need for background story. Simply put, a lot of people don't enjoy big phones. This leads me to wondering- when is a phone too big?

I have a galaxy note 5, which fits perfectly in my hand. Anything bigger and it'd be uncomfortable. 

When it doesn't fit in your pocket. If you're afraid of the phone getting either broken or falling every time out your pocket, then it's too big.

When they stop being able to fit in pockets properly.
When you can no longer hold them single handly up to your ear, and use it as a phone.

We re basically at the limit now of what phones should be in size.
Any bigger and we reach impractical sizes.
Any thinner and they break to easy.
Also reaching the point where their fast enough for any "phone" like funktions you could think of.

Time to just make the battery life better. and the phones themselves cheaper.
I think at some point smart phone industry is going to slow down drastically.
Maybe a crash is comeing.

It's about girth

Anything more than 6 inches on a phone is too big for my liking.

Mines 5.5 inches, wouldn't want a phone too much bigger then that. At least half an inch smaller than your manhood is a good judge for max phone size.

Above 5.1' for me. I used a 5.5 for a while and it just wasn't a good experience

My actual phone is 5.1 inches and I find it extremely comfortable (I have pretty small hands) but I think anything more than 6 inches is too much, that's phablet territory (and hell do I hate phablets)

Depends on the person.

I'd like to say it's too big if it doesn't fit in your pocket but there are taller people than others that their pants also have bigger pockets.

As well it all depends on their comfortability when holding the phone. (We've had forums about gaming controller sizes and we know it all depends on the size of gamers hands, phones should be no different)

Personally anything bigger than 5" phone is too big for me.

Basically this.