If we look at it rationally, the phone numbers were an extra complexity layer introduced by technology. The smartphones solved that problem rightly so. You just have to member the person's name, rightly so.
I don't think that's any more rational than suggesting smartphones supplanted memory training; the phone number is an implementation detail, the lack of practicing memorization of important information is a general case. Smartphones created a dependency on themselves and solved problems that mostly weren't problems, or were often tertiary optimization problems before they came along, while phone technology actually solved a fundamental problem with high-latency communication via mail.
If I ask myself whether I'm generally better off having my contact numbers in my smartphone vs before—which itself is a fictitious premise, since mobile phones had them before they got smart—the answer is definitely "no", because the distribution of people I call isn't so varied as to make memorizing them difficult, but my lack of inclination to do even that means I don't remember the most common case and always need to have the phone or I'm screwed.
It's hilarious to watch this play out with drivers who are entirely dependent on a Maps app for directions in their own city. They don't remember basic routes, address blocks, can't even do it sometimes without the phone speaking it to them. It wasn't really a problem before, you'd just figure it out most of the time, or ask someone for an approximation.