Q: Why doesn't some of my music sync to iphone?

Hi lsgknits,

Thanks for using the Apple Support Communities! I'm sorry to hear you are having these issues with your iPhone and iTunes. If you are having issues with specific content not syncing, you may want to double-check that none of the following options are selected:

Keep items from being automatically synced

If there are some items you never want synced (for example, if they’re too big to fit on your device), you can keep them from being synced. 

You can also turn off automatic syncing for music, movies, and TV shows. You must do this if you want to sync iPod classic, iPod nano, or iPod shuffle with more than one iTunes library, or automatically fill your device with songs using Autofill (see the next task, below). 

1. Connect your device to your computer.

2. Click the device button, then click Summary.

    

   

3. Do any of the following:

    
    
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     Keep individual items from being synced: Select “Sync only checked [items].” Then, deselect the checkbox next to any items in your iTunes library that you don’t want synced. 

      
    
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     Turn off automatic syncing for music, movies, and TV shows: Select “Manually manage music and videos.” 

      

4. Click Apply.

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

You may also want to see if you are able to manually sync those specific items:

Move content from iTunes on your computer to your iPhone, iPad, or iPod touch - Apple Support

Regards