Sync only favorite songs from iTunes to iPhone
Create a playlist with your favourites.
Connect your device to your computer and click the device button near the top left of the iTunes window.





Select the type of content you want to sync (for example, Music or Apps) in the sidebar on the left.





Select the Sync checkbox, then select the items you want to sync automatically each time you connect your device.





Chose Selected paylists, artist, albums and genres.
Select only the playlist created on point 1 and apply.


iTunes 12 for Mac: Sync iPod, iPhone, or iPad