Talking of plain English
As an "adequate replacement timepiece" a mobile phone is less usable than a pocket watch on a chain - which the wristwatch, for good reason, replaced.
Mobile Phone: Occupy free hand to retrieve from pocket, open case, press button to light screen, read time, close case, replace in pocket.
Wristwatch: Twist wrist to face owner, read time.
Even without a wraparound case on the phone, it's still not really in the same league for usability.
On the other hand (!) it's not like the current time is unavailable, there are clocks everywhere, on home entertainment devices, computer screens, kitchen appliances, car dash, street advertising, office walls etc; so it's not like the ordinary man in the street depends on the church clock any more., plus the time is the same information for everybody in any one location. The personal notification alert is becoming the more important piece of information, which is where the convenience of a quick glance at your wrist is more useful than many who have not tried it yet realise.