No, that is not possible at this time (at least from my own experience). Currently, you can make changes on your iPhone, but in order for you to make changes to the same document on your Mac, you first have to:
-1) Download the file from your iCloud account
-2) Make the changes from Excel or Numbers app on Mac
-3) Save the document in Excel or Numbers
-4) Then, go back to your iCloud account online (on your Mac), and drag & drop the updated file to iCloud
I know I just said a mouthful, but I agree, that is a lot of extra steps for making a document sync on both your Mac and iPhone.... Hopefully Apple will have a solution for this in the future (where, for instance, a document can be accessed via iCloud directly from an iWork application (like Pages, Numbers, Keynote), and then we are able to make changes to the document, and as changes are made, it automatically updates in iCloud without us making any additional steps, if this makes any sense)....
Hope this helps....
Appreciate the reply. You mentioned iCloud... what about through iTunes, which is what I'm trying to do?
It looks as if it should work, yet...
I tried copying the revised file on the Mac into the iTunes window and replacing what's there, but even that doesn't work via synching!
One has to manually use the + sign in Numbers on the iPhone and manually copy the file in. And, if it already exists (as it does), it then creates a 2nd version of it!
Does the Numbers spreadsheet behave differently? That is, do Numbers files on the Mac automatically sync over to the iPhone when they are parked in the iTunes window for the app?