This page specifies the logic used to auto-format phone numbers in Adjutant.
If there are 10 digits (before EXT or EXT. or X), then format as (999) 999-9999.
If Ext or Ext. or x is in the number, then add to end of number as (999) 999-9999 X9999.
Any phone number longer than 10 digits will not be formatted.