As Steven said, it’s a noun. It’s a compound noun, and you have the same type of structures in Chinese. The meaning would be a manager who supervises the cashiers (one cashier per till). Note that “till” is British English. In America, we say “cash register”. This is a rare example where you really need to use the correct term (American or British) or people will have trouble understanding you.

A "till supervisor" would be a noun in this case. Someone in a supermarket who manages the tills and, I am guessing, the staff on those tills. Just for fun: A till supervisor will supervise a till.

Recently i've heard "superviser" in my construction area in meaning specialist, who controls process.

Hi Siying🙂 I am not sure what have been missed or misinterpreted because I don't have the context but the till supervisor is not a phrasal verb. Good luck 🤞