I think each "friend" has more than one catchphrases so let's list all the other ones they have other than their main ones. Also, each friend has to have a "thing" just like how Joey mentioned in TOW Male Nanny (i.e Chandler's thing is being funny and sarcastic, Ross' is apparently not knowing when to shut up). I'll start...
Joey: "How you doing?" (obviously)
Chandler: "Could I BE any more..."
Phoebe: "Oh no"
Monica: "I know!"
Rachel: "*gasp* Nooooo!!!"
Ross: "WE WERE ON A BREAK!!!!"
Chandler: Math (according to Joey lol)
get it? ok, next?