Is it permissible to use the phrase "so-and-so is the owner of my soul" as a figurative metaphor, knowing that God alone is the owner of souls, by analogy with names such as "Malak" (angel), "Zumurrudah" (emerald), and "Sundus" (fine silk)?

Allah Almighty is the true Owner of the universe and all that is in it, and the ownership of others is figurative. So, your statement "So-and-so owns my soul," if the intent behind it is admiration and lawful love for his knowledge or character, then there is no harm in it. However, it is better not to utter it because it does not conform to reality.