The iPhone camera app lets you rotate, crop, highlight. So you could make a 2nd copy of pic if needed and rotate it. Then upload to your tree. Seems Bromaelor is very strict about "shoulds" though I understand his point that Ancestry is not a photo editor. In Ancestry's acquired software and app, Shoebox (formerly 1000 memories), you can take a pic with phone, crop it and rotate it, then add it to your tree. So I'd recommend adding that app to your phone; it is the same log in as Anc.
I am having the same problem of original poster for uploading from computer though, and will try the resize thing mentioned above. It looks right on computer but switches on Anc. at upload. So will play with photo editors as a later solution if resizing doesn't work.