I agree with the author on a few points:

1. the telephone number system is terrible (but only in hindsight) 2. a telephone number should not be used for security

But his premise of a DNS for phone numbers is ridiculous. Does he think the PSTN was invented when smartphones came out? What about the wide plethora of legacy phones that would cause countless issues?

If someone did manage to complete he herculean (if not impossible) task of making it happen, it would be a massive waste; the PSTN will become obsolete in the not so distant future as internet based solutions take over.