Went for the update today via my Mac and cable - downloaded fine, then all hell broke loose. It wiped device entirely, couldn't update, and couldn't even 'find' phone - so a restore from backup was not possible.
Deja vu moment from last year when the install of 26 somehow coincided with a completely fried logic board. They said total coincidence, but really? Their install of new one did the same, so they gave up and handed me a new phone.
Today, it was another visit to Apple Store, where techs were able to strong-arm iOS back onto device and a slow restore from iCloud (from a backup yesterday, thank goodness) brought device back to life. Tech - while helpful, called it a 'glitch'. I have other words for it.