In case anyone asks you to implement any input formatting, see if you can get them to change their minds. IMO the most bug-prone and useless feature of websites. Let the user put in whatever they want and just input.replace(/[^0-9]+/, ''). You, your users and your product owners will be happier.
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=...
