There is for now no way to add custom fields easily.
If you are familiar with php and sql you will have to edit the database structure, the functions to get members, and the shortcode generated code (and admin panel and edit/create member if you don't want to edit phone numbers directly in database).
Other ways use existing data for other purposes:
If you don't need the website field you could use it to display phone numbers and update shortcode to remove the link tag.
Without the flipping effect you can use the description to add phone numbers.