transfer my music to iPhone

There are a couple of options:

1. Use iTunes or Finder and sync the music directly over USB cable or Wi-Fi: link-> Use iTunes to sync your iPhone, iPad, or iPod with your computer - Apple Support
2. If subscribed to Apple Music, you can use iCloud Music Library: link-> Turn on Sync Library with Apple Music - Apple Support

Badgad,

If you have a subscription you can use cloud syncing. If you don't have a subscription, you can connect your phone to your computer via USB and sync. See information in here:

Sync your iPhone, iPad, or iPod using your computer - Apple Support