"Do you have a phone?"
Translation:너는 전화가 있느냐?
It's an interrogative verb ending, i.e. one which forms a question. It's also quite blunt (I'd say even more so than if you use the -아/어 form), so only use it on people you don't have to show any respect to, never superiors and not on equals either unless you're really close friends – or trying to pick a fight.
So like would parents ever use this Or perhaps security forces during interrogation?
You don't use this form when you are saying, it is VERY rude. It is an extra-informal informal form, now what I mean is it is informal-informal form. It is usually used when the master asks their slave or their servants, and when the king talks to their subjects.
I thought that 전화 meant something along the lines of "calling" someone on the phone as in "전화 해줘" -- is there a difference between the word for "phone" and the word for cell phone (i.e. 핸드폰)?
전화 is used for both the physical phone itself and for “phone call”. This is one difference to 핸드폰 which only refers to the device (i.e. you can't say 핸드폰하다). The other difference is that 전화 is a more general term which can refer to cell phones as well as mobiles. 핸드폰 on the other hand only refers to cell phones.
Seriously? Why is it '느냐'? OH MY GOSH IS A KING TALKING TO THEIR SUBJECTS? OR IS THE MASTER TALKING TO THEIR SERVANTS OR THEIR SLAVES? THE NATIVES ARE GOING TO LIKE IT WHEN THEY HERE THAT! I KNOW, BECAUSE I AM ONE!
Yes, although in my experience it is more common in historical settings. In modern ones you are more likely to see -냐. Still, I would advise against using it except to children and maybe the very closest of friends as it tends to sound like you’re talking down to somebody.
you can find dozens of songs using this plain form. It comes to my mind now 2 of them: Bae bae (BIGBANG) and Fiancé of (MinO). I learned english just by listening to english songs, but this cant be done with Korean, this is one reason for it. In Fiancé you kinda of understand the usage of this form, but in Bae Bae i really don't understand why they use it.