6+ 8.1.3 can not rotate even on Standard view

just noticed today that my iphone 6+, 8.1.3, can not rotate, tried everywhere on phone can't find what it was on ipad or earlier version such as using volumn button to rotate and lock the screen. searched old post, seemed this problem has persisted for a while, some people suggested not using Zoom would fix the problem, well, that was not the case for me. I'm on Standard and I tried both Zoom and Standard, tried my browser (lock and unlock screen), all failed.

is there any way to fix this or is this just apple's bug that can not be fixed that we just have to suck it up -- passed the return deadline, or anything we, I could do?