It's a twisted-up version of the phrasal verb "to f*ck with (something)". The main verb has been changed to "funk" (in reference to funk music - an extra meaning is added), and softened even more by using a "ph" spelling. The basic meaning of "interfere" is meant, but with the music reference, we understand it as "play with". Its use is limited to only this song.

Don't Mess with My Heart is what it means. in english "phunk" is usually spelled "funk" , I also believe that phunk is a word that could be replaced with the F*** word in Englsih. ( swearing word. )

It means Don't mess with my heart )

:-D.. I heard it in black eyed peas's song but I couldn't make sense that phunk means f*ck.. :)

Extreme, "Get the Funk Out". Can I stop now? :)