OP gave me instructions of what to do for any of you who are pretty inept at that kind of stuff like me:
"Here are the steps:
• First the idea is to get the back casing off. You have to remove several screws.
• Once the back panel is removed look at the headphone jack itself. (Note, the LGG3 is capable of handling headphones with a command button, so if you look at your headphone's connector (the bit that goes in the phone and assuming your headphones have a button) youll notice 3 distinct sections. These are button, right, left, and ground in that order (i think?))
• You should notice there are four copper(idr what metal?) leads that extend from the headphone and touch corresponding metal plates on the body of the phone. These are the problem. It is a stupid design. Those leads touch the headphone jack by simply a pressure connection. Basically, they are relying on the metal leads bending against the headphone jack. Imagine pressing down on a diving board. the strength of the diving board will make sure that it constantly touches your hand with some force, right? Now imagine that suddenly the diving board got old and just started to sag under its own weight, assuming you don't push down anymore, you won't have as good of a contact with the diving board.
• This was a long winded way of simply saying that the metal leads arent bending against the headphone jacks like they should meaning they have a weak electrical connection.
• you have two solutions. The first is to remove the headphone jack (its literally only stuck there by a cheap adhesive.) Then manually bend the leads out more (like restrengthening the diving board) and put it back. This is easy, but not permanent. However, it worked for me for the duration of my time having the phone. your second solution is to solder the headphone jack to the leads on the board. I didnt try this (its really really difficult to not melt the headphone jack plastic), but its a good way to ensure the connection stays even if you jostle the phone a lot.
after that it should work again."
I opted for the bending copper back into place method. Very easy, took about 5 minutes, the headphone jack box comes up pretty easily and I just bent the copper connection away from the box with a flathead screwdriver. Put it back in and it worked perfectly.
TL;dr OP is a great guy <3