How to import MP3 files to iPhone's music library?

I already know how to do this with PC/Mac; does anyone know of any apps or techniques that could directly transfer an audio file from, say, Google Drive into the music library, only using an iPhone? For purposes like inserting audio into videos with apps like iMovie.

The only way to transfer music files to an iPhone is using iTunes because you have to sync those files between your computer and your phone.

A bit of advice. Next time you get a phone buy Android instead. Then you can simply plug the phone into your computer and copy files back and forth as if the phone is a USB flash drive. Easy and you no longer have to use a propriety program just to copy files to your phone.

Bring the audio into iTunes, synch the iPhone, then iMovie on the iPhone can get to the audio. Works the same way on my iPad.

The iPhone 6 doesn't have Bluetooth, so transferring MP3 files will be problematic. It doesn't have an SD card either.

Just add the mp3 to your itunes song list, then copy to iphone. Simple and I do this all the time with MP3.

I do it intwo ways.
Way 1: Get it on iTunes. Firstly, MP3 fiels are in the computer, download iTunes to computer, and turn on it. Drag the files to iTunes Library directly. Then sync forom your iphone. You can play the music on your iphone. (Note: you can't delete the local files on the computer, otherwise, iTunes library will fail to play it.)
Way it with FoneTrans. Download and run it on your computer, then connect your iphone to computer, then you can see your iphone's data are showed up in the interface. Click Media- import to your iphone from PC. It's very easy and fast to transfer.
There's fre trial, you can download it.

You need to use itunes to sync mp3 to your iphone