The issue actually isn’t a problem on your operating system or on the message board - the images are actually on their side. Your phone will include “metadata” that your photo viewing software will read to auto-rotate it to the orientation you intended. Some software (like Facebook) will read that data, but the message board (vBulletin) doesn’t. It displays the actual image, which means it may be on its side.
The best solution, at the moment, is to use an online image rotator to get the picture to the right orientation - there are a bunch of free options if you google “online image rotate”.
We may be able to find a plugin to add this functionality to the message board - I’m going to do some digging on my side.