A phone number is definitely not a number - for example, it can often be written as starting with a +. Not only that, but one number can have multiple valid exp

A phone number is definitely not a number - for example, it can often be written as starting with a +. Not only that, but one number can have multiple valid expressions (eg. a number with and without a country code). That's ignoring the different ways people like to format them (spaces, dashes, letters, etc.)