A word or phrase that someone says frequently is called what? As an example, a friend says the phrase "Faithful God" frequently, say 15 times in day. So, what English word defines the term "Faithful God" with respect to the friend?
If it's something distinctively his, to the point where bringing it up in conversation with Friend #2 causes him to laugh and say, "Friend #1, amiright?" it's a catchphrase.
A catchphrase (alternatively spelled catch phrase) is a phrase or expression recognized by its repeated utterance.
A similar idea is the signature phrase. It's less condescending and simply expresses the idea that that idiomatic expression is strongly associated with that person. If you're expressing how fond the friend is of his own turn of phrase, you might use pet phrase.
old saw TFD idiom
An oft-repeated saying, maxim, or proverb; a cliché or hackneyed expression.
My dad has a few old saws he never hesitates to share with my kids whenever we come to visit.