The Callback hyperlink is not obvious as it is grayed out.
The Caller also has a shorten hyperlink that is very small and difficult to tap (refer to first screenshot). The person who receives the call gets a full phone number hyperlink, which is easier to tap (please refer to second screenshot).
1) Request that the callback hyperlink is Blue to indicate a hyperlink
2) Request that the callback hyperlink is always the FULL phone number for ease of tapping (not just the small phone icon).