Input Mask format consists of literal display characters (such as parentheses, periods, and hyphens) and masks characters that specify where data is to be entered as well as what kind of data and how many characters are allowed.
Step 1: Create a simple form
Create your own form including a phone field
Step 2: Phone number field
Edit Phone Number Field -> Setting Tab -> Input Mask -> Click Enable -> fill out your format
Mask: Click the field where you want to create the custom input mask.