How to get music from itunes onto my iphone?

I have an outdated version of itunes and I can't update it because the newest software for mac does not run on my computer. I want to know if there's an app or some type of way I can get the music in my itunes transfered on my iphone? I have a lot of music on there that i didn't buy or find on the web so I would like to have it on other devices.

I have an SD adapter on my old MacBook Pro, I connect a miniSD chip through the miniSD to SD adapter that comes with the chip, select the tunes I want and drag them into folders on the miniSD chip. I create separate folders for each album to avoid conflicts. I have them all as subfolders in a folder called music. I then unmount the chip, plug it into my phone and it's all there including the artwork and lyrics. If I'm just sending a single song over, I drag it out of iTunes, drop it on my desktop, go to my bluetooth file transfer utility and send it to the phone, then I bring up my file explorer on the phone and move it from the bluetooth folder to where I want it on my microSD card, again all the artwork and lyrics comes with it. Since iPhone doesn't have a microSD slot, you'll have to either bluetooth it over or connect the iPhone directly to the Mac at which point iTunes should be able to transfer it for you just as it would for an iPod, but iTunes also observes the DRM so you may lose access to the tunes on your pc as it may think you gave the tunes to the iPhone. If you can connect the phone as a data drive, then you could just drag the tunes out of iTunes onto the phone rather than trusting the magic of iTunes.