oh, and it's "Kop khun khap/kha"
kop - thank
khun - you
khap - if the speaker is male. equivalent of "po/opo" .."krap" formal
kha - if the speaker is female. ditto.
beware though that 'kop' is not stand alone, unlike the English equivalent. say the whole phrase, otherwise 'kop' would mean "frog".
pwede ring "kop chai" na lang. especially if you're speaking to a younger person.