Hi Lisa! Great question.
There are a few approaches available here but I’ll limit my response to three considerations:
(1) Provide your client with examples of how you want the suggested revisions to be delivered. This can be done informally or you can incorporate the example(s) into your agreement as an Exhibit.
(2) Define how the client can communicate with you. You can write into your agreement that revisions/feedback must be delivered a certain way (e.g. email or through the use of some collaborative platform), and that any communications outside of the defined method are not binding and will not be required revisions.
You can always assure your client verbally that you’re available for collaboration (as much or as little as you like) but, generally, you are able to narrowly define the acceptance process (including how the client provides feedback to you).
(3) Define the timeframe during which your client is able to provide the revisions/feedback. It’s very important not to have open-ended client-obligations. From what I read in your post, each “Round” of revisions is defined in your agreement by substance (i.e. the desired content and specificity of the revision/feedback) but you might consider taking that a step further and adding temporal limits as well. For example, you might include that the client has ten days to provide feedback for each Round unless you agree otherwise, and if no communications are received, the client has accepted and approved the work product as it was delivered.
Hope that helps and please feel free to ask any follow-up questions!