Valid numbers and real numbers are not necessarily the same thing.
You can have a valid number which is not a real number.
This community post should point you in the right direction for custom validation with RegEx.
If you want to further make sure the number is real, you’ll need a 3rd party that can actually make the check for you and return a response.
There are a few 3rd party services that do this kind of check for the US and UK. There are probably some that do it for New Zealand as well.