iPhone ceased connecting to AkrutoSync on laptop with static IP address
Thanks to AkrutoSync, the problem is solved.  The WiFi was off, so internet connectivity was due to the use of my data plan.  The iPhone often flips settings in ways that I don't expect, e.g., switching out of low-power mode.  It's still possible that I had disabled WiFi, but at the moment, I am unable to think of a situation in which I would specifically choose to ensure that the data plan is used instead of WiFi.

Afternote: Actually, one reason to ensure use of data plan rather than WiFi was to ensure uninterrupted connectivity as one moves around, e.g., when using Google Maps for navigation.  It was possible that navigation would be uninterrupted by the hand-off from WiFi to data plan, but as I was in a hurry, I didn't want to risk it.