Obviously, taking a phone in both hands and purposefully bending it is not part of normal use. Nevertheless, it is a good test of rigidity. So I decided to test other items.
I dropped a dinner plate from a height of one foot onto a counter top. It broke in two! I now have seven plates rather than eight.
I dropped a wall clock while I was attempting to reset it. The glass shattered. I removed the glass shards, vacuumed the floor, and bent the hands so that it would work again, but the face is unprotected. (From what, I don't know)
I drove my car over a nail in the street. It penetrated the tire and the tire deflated. The tire was unusable but, the manufacturer replaced it, even though it wasn't an Apple tire.
Some lady drove smack into the front of my car (!). The front end was all smashed up. Not as substantial as it had looked.
I dropped my iPhone 5 on the sidewalk and it disassembled itself. Since this betrayed an internal defect, they did not charge me for a replacement phone.
After all this, I have decided not to take my iPhone 6 Plus in my hands and bend it to find out if it is fragile. I'd rather have a phone than a pyrrhic victory.