The phrase "von klein auf" supposedly is a fixed phrase meaning "from the early age":
Wir sind schon von klein auf gute Freunde.
My question is, why is "auf" in this phrase? Wouldn't "von klein" make the same sense? If I would leave it out would it be comprehensible?
Small note: Of course I know that fixed phrases are fixed phrases and there is not much to them. But even so, most of the time I understand their grammar and it helps me form other sentences. For example, I know the fixed phrase "Es gibt...". At first I didn't know the grammar because I was taught it as a fixed phrase. But now, I remember conjugation of "geben" thanks to it.