help

I can't think of any case where we would say "common of phrases". What do you think it's supposed to mean? "Common phrases" consists of an adjective and the noun it modifies. English doesn't do adjective+of+noun, it does adjective+noun.

It's a stretch but "Common of phrases" could mean typical of verbiage: "Such sentence construction is common of phrases applying to the introduction of a novel feature"

"Sorry about that" used to be a common phrase. At one point, it used to be one of the most common of pharases. It works as a comparative, since commonist doesn't always sound quite right.

God forbid they should confuse us poor commoners with commonists. Life is hard enough!

It does sound like some kind of leader of the proletariat, doesn't it?

Good one Rog