The only way I've seen so far to add multiple phone numbers to a contact is through the Contact UI. I believe adding support for updating multiple telephone numbers through automation would be extremely helpful.

I'm envisioning using the existing "Update Contact Field" action, but instead of phone being a static field, have it accept an array of values. Another option would be to have separate fields for each label, but that would limit you to only 4 phone numbers. Open to suggestions or thoughts.