Hey David, are you talking about a linked version of the telephone number so that someone can click it to call? I believe this is something that is done automatically with certain email readers/platforms, not necessarily something that you would do within your email (unless you already have something in the HTML of your email blocking this from occurring).
Yes, I am speaking to the linking of phone numbers.
Right now I have two phones numbers (Not linked) listed in the body text of an email, and when I view the test on my mobile, the phone numbers are not appearing at all.
If the phone numbers are not appearing at all, is it possible that your links are set to show as white (or whatever your background color is)? This would be in the HTML of your email. You can test this by touching where the phone numbers should be, and seeing if they're linked but just in white.