While it is possible to do this, there is no way to preserve these modification after an update and you will have to repeat this every time we release an update. 

Here is what you need to do: 

Step 1: Please edit vamtam-editor/shortcodes/config/team_member.php and duplicate this code: 


   'name' => __('Phone', 'wpv'),
   'id' => 'phone',
   'default' => '+448786562223',
   'type' => 'text'


Step 2: Please change the 'phone' id to 'fax'     

Step 3: Please edit vamtam-editor/shortcodes/handlers/team_member.php and again, duplicate this line and change phone to fax: 'phone' => 'fax'
(this step can be preserved after an upadte) 

Step 4: Get a child theme from https://vamtam.com/child-themes/ and copy templates/shortcodes/team_member.php from the main theme to the child (remember to create the missing directories). In the newly copied file insert this after line 48:    


<?php if(!empty($fax)):?>
   <div class="team-member-fax"><a href="fax:<?php echo esc_attr( $fax ) ?>" title="<?php echo esc_attr( sprintf( 'Fax %s', $name ) ) ?>"><?php echo $fax?></a></div>
  <?php endif ?>