This should probably be discussed elsewhere, but, I don't know if I like just disabling it if there's something not 0-9. If you attempted to type +255 123 12314 it would ignore the + and spaces and put "2551231234" into the box. I think I would prefer the user experience of stripping things that are so commonly going to be in a phone number. Any time you ever paste an international phone number into this box, for example, you're almost guaranteed to have a + and will also have some spaces. A domestic U.S. number might be of the format (123)123-1234. So giving them an error and forcing them to paste somewhere else and edit out these characters isn't the best.

So my point is, maybe strip these characters instead of just giving an error ( `+`, `-`, `(`, `)`, and space). Could show a little message saying phone numbers must be digits only and we have attempted to convert what they entered.