How do I sync MP3's from my MacBook to iPhone?

I haven't used MP3's in years, but recently bought some on my MacBook (on an independent site, not iTunes) that I need to sync to my iPhone. And I cannot figure out how to do this. I've looked through all the settings on both devices and even tried using a cable, but nothing seems to work.

This page says "If you don't subscribe to Apple Music or iTunes Match, you won’t see an option to turn on Sync Library." — Turn on Sync Library with Apple Music - Apple Support

Is this real life? That would be ridiculous. I don't have any need for Apple Music. Are they seriously not going to allow me to sync my MP3's to my phone without paying for something I will probably never need again. Im simply looking to sync 3 MP3 files.