A phone number is presumed to have some level of identity proofing behind it (i.e. control over the phone number means you have a credit card, bank account, photo id, etc.).

As the article points out, this turns out to be rather easy to spoof.

How do "oh by" codes solve this issue? What if I print up a bunch of business cards with 0xJOHN?

Identity proofing is a hard problem!