Each contact will have a details card where you can view and manage your contact's information. Under the heading Contacts, you will see the phone numbers and email addresses associated with the contact.
To make changes to a piece of contact information, click the icon to the far right of the contact to edit. This will open a sidebar where you can update or delete an existing contact.
The contact marked as the default will be noted with a checkmark and is the piece of contact information that will receive campaign followups.