You can tell Google in your HTML markup to ignore a section of HTML.
<!-- googleoff: all-->
<a href="mailto:user%40email.com" title="email user">firstname.lastname@example.org</a>
<a href="tel:+123456789" title="call user">+123456789</a>
<!-- googleon: all-->
That will prevent that piece of HTML from appearing in the cache or being indexed. It offers no security and is only supported by Google.
Alternately, you can do the opposite and share contact information in a way they can index more effectively. Using the hCard microdata format.
The only way to prevent webcrawlers from accessing this information is to only show it to authorized user sessions that have been verified as humam. Even that is a challenge.