The docs say:
The AWSPhone scalar type represents a valid Phone Number. Phone numbers are serialized and deserialized as Strings. Phone numbers provided may be whitespace delimited or hyphenated. The number can specify a country code at the beginning but this is not required.
What determines whether a given string is a valid AWSPhone? In addition, is there any safe way to generate (possibly a large number of) AWSPhone test values that are guaranteed to be valid but assuredly are not in-use phone numbers?