Please correct me, is it right that restaurant waiters ask 以上で? to mean "is that all" after you order?
If so, I can see two opposite logics behind it:
First logic: The basic meaning of 以上is "beyond, further", as in "something beyond?" or "nothing further to say?", so that's the implied question. Or else, 以上 can be translated as "more than" as in "anything more than that?". The waiter asking 以上で？is asking you what else you want something "on top of" what you already asked for (以上で何?) .
Second logic: Maybe possible extra orders aren't thought of as added "on top" of the previous ones (as we do when we pile things up), especially as Japanese is written top down (縦書き), which makes a list of desires particularly likely to be perceived as extending downwards. if so , 以上で is perceived as meaning "the abovementioned" and the omitted phrase isn't "what" but rather "is enough" as in 以上の注文は全部ですか?
There probably is some conclusive proof that one of these two logics is wrong.
On a practical note, how should I phrase my answer to the waiter's question, both when I have nothing to add and when I would like to ask for something else?