How to format the phone number to be like ###-###-###?

I have checked your form and I can see you have already set up  a mask to the phone field: 

There are also some widgets that will help you to capture the phone number and apply a format based on the country or region selected, here're the links: 

https://widgets.jotform.com/widget/international_telephone_picker

https://widgets.jotform.com/widget/phone_picker

https://widgets.jotform.com/widget/country_code

This guide will help you to add the widget to your form: How-to-Add-a-Widget-to-your-Form