How to sync my songs in Music on Iphone to my Mac

I had added songs into my Music Library on my iPhone but couldn't play some of the songs. It tells me "This song is not synced across your devices." I had selected Sync Library on my Music on my MacBook but it is still did not work. I had even left the laptop connected to the phone all night and still did not sync. Fyi, I only have less than 50 songs.