So what I am trying to do is, by any means, transfer one .txt file from my phone to the Raspberry Pi. However, I want to be able to do this without inputting a pin, via bluetooth, that I have to accept with a Raspberry Pi and a Monitor. At the time of the transfer I will have no internet connection, but a wifi adapter is connected. I want this process as headless as possible. Any thoughts?
If you have Apache running in RPi, create an upload form with two buttons: "Select file" and "Upload".
Upload will be done via phone's browser.
It is headless, not sure whether is easy.
If you don't mind keeping a folder in sync as opposed to a specific file, bittorent sync can do that, and here is a link
it does NOT need internet (in fact it works better with local connections)
I don't know about it working over bluetooth (should be possible), but it will work just fine over wifi (could setup a hotspot and either have the phone connect to it or have it connect to the phone)