How does iCloud music determine which songs to sync to iPhone? Let's say I have the following in iTunes


A 100GB library 
iCloud Music enabled
Less than 10,000 tracks


And:


a 16GB iPhone
iCloud Music enabled


Since iCloud Music is now enabled, I can no longer select which songs are synced to the phone:




How does iCloud Music determine which songs from the 100GB library to sync to the phone?
Is there a way to control which songs sync to the phone?
What Apple Music iCloud Music Library does is the following:


It will check all the tracks you have stored in iTunes and
See if they are available in the Apple Music catalog. If not, Apple Music will
Upload them to the cloud. 
All these songs will be available from the Music app on iOS. If you play them, you will stream them from the cloud. If you would like to save songs for offline listening, tap the triple dots next to a song, and tap: Make available offline. 


Because it works this way now, it is no longer necessary to sync via iTunes