There are some default catchphrases that I think are perfect and would never change. These include:
Bob - pthhpth
Klaus - strudel
Alfonso - it's a me
Paula - yodelay
Jay - heeeeeyy (I love this one)
Tom - me-YOWZA
Portia - ruffian (This is so brilliant for a snooty dog)
Velma - blih
Chadder - fromage
Freya - uff da
These are some of my custom catchphrases for my villagers.
Rolf - nosepuffs (I love his adorable nosepuffs... and apparently so do my other villagers, because this is the one catchphrase that the other villagers love to copy more than any other, which can get pretty funny depending on who's currently using it.)
Agent S -

SUPER

(She's a superstar super hero, plus, it makes her sound a little bit like Franky from One Piece, who's totally one of her role models.)
Broccolo - bocci (Just a cute version of broccoli!)
Bettina - cheddar (I thought it was a cute catchphrase for a mouse who enjoys cooking.)
Chops - ma ma ma

(This is straight up taken from Igaram from One Piece... it just seemed fitting.)
Tex - chilly (I thought this was fitting for a smug penguin.)
Flo - breezy (I wanted a cool counterpart catchphrase for Flo to go with Tex's catchphrase. Right now, Ankha is using it, too, because she and Flo are bffs.)