Sorry, I didn’t catch you.
Sorry, I didn’t understand.
Sorry, I didn’t get what you said.
I can’t catch what you are saying.

Pardon?
Excuse me? I beg you pardon?
Could you repeat that, please?
Would you say that again?

Would you speak more slowly?
Could you speak up a little?
Would you speak more clearly?
Would you explain more for me?
Please speak a little louder.
Would you slow down, please?