Updated @sqiller's function for my purposes
CREATE FUNCTION [toolbox].[FormatPhoneNumber] (
@PhoneNumber VARCHAR(50),
@DefaultIfUnknown VARCHAR(50)
)
RETURNS VARCHAR(50)
AS
BEGIN
-- remove any extension
IF CHARINDEX('x', @PhoneNumber, 1) > 0
SET @PhoneNumber = SUBSTRING(@PhoneNumber, 1, CHARINDEX('x', @PhoneNumber, 1) - 1)
-- cleanse phone number string
WHILE PATINDEX('%[^0-9]%',@PhoneNumber) > 0
SET @PhoneNumber = REPLACE(@PhoneNumber,
SUBSTRING(@PhoneNumber,PATINDEX('%[^0-9]%',@PhoneNumber),1),'')
-- Remove US international code if exists, i.e. 12345678900
IF SUBSTRING(@PhoneNumber,1,1) = '1' AND LEN(@PhoneNumber) = 11
SET @PhoneNumber = SUBSTRING(@PhoneNumber, 2, 10)
-- any phone numbers without 10 characters are set to default
IF LEN(@PhoneNumber) <> 10
RETURN @DefaultIfUnknown
-- build US standard phone number
SET @PhoneNumber = '(' + SUBSTRING(@PhoneNumber,1,3) + ') ' +
SUBSTRING(@PhoneNumber,4,3) + '-' + SUBSTRING(@PhoneNumber,7,4)
RETURN @PhoneNumber
END