Project #8 - Build a Telephone Number Validator

This is one of the projects required to earn certification.

Is the phone number provided in the valid format for US phone numbers?

In the US, phone numbers can be formatted in many ways. For example: 1 555-555-5555, 1 (555) 555-5555, 1(555)555-5555, 1 555 555 5555, 5555555555, 555-555-5555, (555)555-5555.