Why are you using Air Drop to send the Music to your phone?
Assuming it started out in Music on your Mac and both your Mac and iPhone are on the same Apple ID, the tunes should automatically be available in Music on your iPhone. Any tunes I add to My entire music Library can be played on any of my Apple devices, including the HomePods and Apple TV, the only requirement being they must be logged onto the same Apple ID. If I don't want to stream the music from iCloud for some reason, I can always physically download it in Music on the other devices when I have a Wi-Fi connection. The Apple Watch is the only device that
requires the tunes to be physically downloaded. It
sounds as if you are trying to drive nails with a screwdriver. (pun unintended)
