Alice is talking about Bob, who will be entering the room shortly. Bob is generally a "nice" character. Alice does not like Bob, and says Bob is "such a phony", but as soon as Bob enters, Alice pretends to be nice to Bob, thus being as big a phony as she claimed Bob was.
For example:
A staple of sitcoms from the eighties to the nineties, but constant reuse has robbed the joke of its sting. You [...] [tvtropes.org]