It started when Reeder, a previously stable app, began crashing frequently. I assumed the app wasn't keeping up with OS updates.
Now several apps are less stable. (Of course I've been shutting down, restarting, etc.)
It could be one app that is having a systemic impact, but my hunch is this is hardware related.
Google tells me this is not a terribly common problem but it does happen. The best explanation so far is How-To: Fix Crashing Apps on Your iPhone and iPad.
The only fixable hardware related cause I can imagine is bad "sectors" on the iPhone's Flash memory -- flash memory defects the OS can't fix on the fly. Memory wear is normal for Flash storage and I expect my phone has a higher than average rate of read/write cycles.
So my next measure is to wipe the phone and reinstall from a backup. During a refresh the OS may have more options for managing bad
This will take some time, so I'll update after I get around to it.
After that, I'll have to bring it in. That's a scary thought!