"Lo and behold," which is a bit archaic but still common coin (if a phrase can be both those things at once!).

Bravo, MG. Your insights on "behold" are a thing to behold.

As to your Q, "Can a phrase be both archaic and common coin at the same time?", absolutely. Our language is replete with Shakespeareanisms and such like, but we are unaware of the antiquity of these phrases.

Curiously, some of these phrases [which we all understand somehow, as tho thru cultural osmosis] make no literal sense to us, but we use them day in and day out nonetheless.

For instance, who does not know what it means to "pull the wool over their eyes"? But how many of us know why this curious phrase made perfect sense in a bygone era?

Can u guess?

And, while we're at it, does anyone know where the phrase "Has the cat got your tongue?" comes from?