sync devices

As I suggested earlier that is probably because Sync Music is enabled on the iPhone. Select the device with this icon in iTunes:

The select the device in the sidebar and then the Music tab. What do you see? If you see a message that iCloud Music Library is enabled then at least for music content is scheduled to sync through the cloud. See Sync your iPhone, iPad, or iPod using your computer - Apple Support to set up sync selections.

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See Turn on Sync Library with Apple Music - Apple Support and Identify cloud status icons in your music library on your Mac or PC - Apple Support. Sync Library, AKA iCloud Music Library, should be enabled in your computer and your devices. Make sure that all of your music is either matched or uploaded. Resolve any issues with content that is waiting, excluded, or had an error status.

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I read that the first time. As noted:

See Turn on Sync Library with Apple Music - Apple Support and Identify cloud status icons in your music library on your Mac or PC - Apple Support. Sync Library, AKA iCloud Music Library, should be enabled in your computer and your devices. Make sure that all of your music is either matched or uploaded. Resolve any issues with content that is waiting, excluded, or had an error status.

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Like I said. See Turn on Sync Library (AKA iCloud Music Library) with Apple Music - Apple Support and make sure that Apple Music is enabled in your library. You need to be using the same Apple ID in iTunes and on your phone.

If there are songs or playlists in your library that don't show up on the phone see Identify cloud status icons in your music library on your Mac or PC - Apple Support and look at the status columns and icons to try to work out why. Content that is marked as error or ineligible won't work and will need a fix or workaround. Playlists that contain ineligible tracks don't sync.

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Do you have Apple Music or iTunes Match?

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yes I have apple music

Is one of your devices unlocked, connected to your computer via a USB cable, and has the computer been trusted if it is an iOS device?

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