"Musica" is an original song by italian singer Paolo Meneguzzi.
It was performed by bassbaritone Kwon Seokyoung (opera singer) and musical actor Ko Eunsung during Phantom Singer's duet battle. They won the battle and moved to the next round.

English and italian aren't my first languages, so if you think some parts of the translation could be better, don't be afraid to leave a comment ^^

Enjoy!