Many email clients (including Gmail and mobile devices) will automatically transform phone numbers into links. Prevent this behavior using the zero-width white space character (​) Instead of this:
Inject the zero-width white space character anywhere in the number to trick the email client and prevent it from turning the number into a link. I like to put it in the middle:
This Litmus compatibility test shows that it works great in all email clients, including Outlook and Office 365. It works for different format variants and international numbers as well.