I'm not doubting that the phone went funky after the update, I'm just not sure that the update caused it. I don't mean to be cynical, but it's possible that the "expert" made matters worse.
I was getting the BSOD on my iPhone 5S only two or three months after I bought it. It turned out to be an Accessibilty setting that was causing the blue screen crash and the phone to reboot when I would try to access any of the help sections in all three iWorks apps, Pages, Numbers and Keynote. When I turned that setting off, everything was fine.
My anecdotal experience doesn't help you at all. I'm merely trying to say that there could be any number of reasons why the phone is crashing that have nothing to do with the update at all.