Changing format using javascript
HTML
<script src="//digitalbush.com/wp-content/uploads/2014/10/jquery.maskedinput.js"></script>
<input name="textfield" type="text" id="textfield" value="6267973685" />
Enter number like this and in next field it will display like this
<input name="textfield2" type="text" id="textfield2" value="(626) 797-3685" />
JavaScript
$("#textfield").mask("(999) 999-9999");