Added phone column and tests.

A couple of questions:

1. I defined an enumeration on the PhoneColumn class that defines the types of phone numbers that seem to be supported. Is defining the enum on the class okay, or would you like it in a separate file?

2. What should happen if an invalid/unknown/new phone_type is returned? Currently, I set the value to "None" instead of failing. I'm going back and forth on this decision.