In the LiveCycle Designer, you can use a phone number field.
To add the Phone Number field and validation:
- Open your form in LiveCycle Designer.
- Click Insert -> Custom-> Phone Number. You can choose UK or North America
- In the field tab of the properties window, specify the Max Chars for the phone number.
- Click patterns. In the validation tab, select type and click apply.
- In the value tab, specify custom messages.
You should be able to add the validation. Let me know your thoughts.