I don't know if it's really that remarkable .. I don't think we can really attribute losing one specific type of memory over an entire civilization in about one generation such a "bad" thing.

The phone wasn't a household staple for pretty much the whole of humanity. It's really only been about a single generation (well, maybe 2 generations at this point) that the telephone to which you had to remember phone numbers was an important thing. Even in the early 1900's you would pick up the phone and an operator would answer and you had to ask them to connect you to a specific place/person.

And given that there 21 year olds alive today who never had a land-line (or even cable television) in their house or have even seen a dial phone, across the world, and that's only increased, it's not that surprising that we don't choose to actively remember phone numbers anymore .. it's just not "built in" to our core abilities yet because it was never something we needed to do on any type of evolutionary or generational scale.

I don't necessarily disagree that, on a whole, many people rely on technology so much that it has made them blind to the world around them (like so many who can't even read the map on their phone without blue lines telling them where to go). But I do think that not remembering every single phone number isn't something to really be concerned with at the human level .. not to say we shouldn't be teaching the importance of remembering certain numbers for emergency purposes though.