The most common reply is:
It's pronounced /pah-ZHA-loos-tah/ and means "You're welcome" in English.
However, I must note that when the girl explains the word by syllables she says /po/ instead of /pa/. She reads the word properly only once in the very end (when по- sounds like /pa/). This is because O sounds like A when it is unstressed.
By the way, "Большое спасибо!" means "Thank you very much!".