Is there a key for entering text on ipad mini for the schwa symbol?

Since for the most part, schwa is a phonetic symbol rather than an actual part of the alphabet, not likely. It is certainly not available on the English, French, Spanish keyboards on iOS. It is possible its available on one of the keyboards (although technical it wouldn't be schwa, just look like it), but not sure which would be good candidates.

You're welcome.

It is possible there is an app containing a phonetic keyboard in the app store (or not). I haven't had use for one, so have never checked. Using it would require some copy and past on your part. But it might worth a search.

Oh, just to be clear (should have googled and not trusted my aging memory) you're basically looking for an upside-down "e", right?

I Have copied the text here and entered it into my keyboard shortcut as phrase and made the text to equal uhh - Ə ə æ