Welcome, @K_M,
I’m afraid there’s no way to dissociate completion of the task as a side effect of all of Approve, Request changes, and Reject.
When using the Approval task type, I find it’s best to do so as a subtask of the actual work task for that reason (and then, too, it’s easy to permit multiple approvals):
For a workflow as you described, I suspect right now with current rules functionality and this Approvals task type behavior, you might instead want a single-select custom field to use to designate your phases/approvals and automated based on that.
Hope that helps,
Larry