This doesn't work for phone numbers if you want to do something programmatically with them. In Germany it's for example common to include the international prefix _and_ a trunk prefix like this in written phone numbers:

    +49 (0)30 23125 123

Your naive approach to just replace non-number characters would lead to an invalid number in such a case. Using libphonenumber you'd get a correctly normalized phone number while the user doesn't get bothered for inputting a technically invalid number: https://libphonenumber.appspot.com/phonenumberparser?number=...