Due to the ever increasing sizes of phones that are released nowadays blurs the line between. Have you ever really heard the word phablet thrown around nowadays. Even the small Android phones are kinda dead and when people want a small phone they would usually just go for an iPhone nowadays.
ps. By the way my dad got a hold of a iPhone 4 for about 90 Bucks AUD and holding the phone compared to my OnePlus One feels tiny.
I've heard it for phones over 5.5 inches. everything below that now-a-days is not considered a phablet. like 5.2 inches or something like 5.3 it's just considered normal sized now.
In my personal opinion the only phones i consider phablets (personally) are the Xperia Z Ultra (This phone was 6.3 inches) the Samsung Galaxy Mega (6.3 inches) HTC One M7 MAX (5.9 Inches) and the Nexus 6 (Of course 6.0 inches)
I am pretty sure the word is actually "Fablet", where the 'T' (for 'Tablet') is changed for an 'F'...not a 'Ph', like the word Phone is what you are referring to.
My understanding of the word "Phablet" is for when someone uses a tablet as a cellphone, which I have seen someone actually do in a restaurant, which has to be seen to be believed. THAT in my eyes was a Phablet in action. An over-sized phone on the otherhand, that is typically used by girls and bejeweled to death, is called a Fablet (because it's 'Fabulous').