Instead of finding what is the type of input, you can restrict the user not to type characters in Phone No field.
Place the below code in Change event of the Phone No field with Java Script as language.
// restrict entry to digits
if (xfa.event.change.match(/[0-9]/) == null)
xfa.event.change = "";
Note: You have placed the question in the wrong forum.. You might need the Designer ES forum.
Thanks
Srini