In reply to:
how to get the cursor to automatically move to the next field when a user is typing in a phone number that is broked down into 3 separate fields
This can only be done with client-side scripting. You will need to test to see whether or not the correct number of digits have been entered into a field, and then set the focus to the next field.
Setting the focus in JavaScript is quite easy:
document.formname.fieldname.focus()
You'll need some sort of loop structure based upon an onchange() event; however, it would be much better (from an accessibility standpoint) to use only a single field for a telephone number.