I agree with Imz Miah. "To coin a phrase" is to invent a new expression. (Sometimes these expressions are used only once; sometimes they become part of the language.) You, Imz, and I are members of this website. So we are italkiERS! (Look! I have just coined a phrase!)

"To coin" in this example means to create something usable (eg. currency).

"coin a phrase" Coin can never have a single side .. Girl/Female are incomplete unless she has man in her life

I've always thought "to coin a phrase" means to invent a phrase or be the first person to use it.