1. Go to Setup>Develop>Sites>Click on the Site Label for the SUMO Site (SUMO Voice Reminder?), then click on the “Public Access Settings” button.
  2. Here you can control the profile for the guest user license.
  3. Scroll down to the Field-Level Security section and click VIEW next to Contact.
  4. Click Edit.  Find the field.  And check the Visible checkbox next to it.
  5. Save and you should be good.