Point is: I very rarely upload photo's from my iPhone. I nearly always use genuine digital camera's (of Olympus). These images get corrupted too. But only the thumbnails of the portrait oriented images in the galleries, not the original ones. What has that got to do with using 'wrong' photo editors?
I suspect the thumbnails are created and stored at the time the images are uploaded, so perhaps a problem lies in that process. So I am curious -- in these portrait oriented images that exhibit the problem, do the intermediate sizes 'small, 'medium', and 'large' also appear rotated when the thumbnail is wrong? (There may not be a separate link for 'large' unless the original is larger than a certain size.) That could offer a hint whether the problem is with the initial upload or in-line processing as the gallery displays are built.
As to right vs wrong editors, it is difficult to do more than speculate, but it could be some custom/manufacturer-specific fields might deviate from the JPEG standard and confuse the parsing of the header data. I'm afraid I do not know much about the internal structure of JPEG files. I would expect an actual data corruption (e.g.; "hardware error" or missing bytes) in the file upload process would produce some sort of error message with no image visible, but perhaps I'm guilty of unwarranted optimism.
I admit I haven't been using PBase as heavily the past year or two because of other activities taking up my time, but I have uploaded probably 200 or more files in the past 12 months and have not encountered the problem you describe. (Which of course does not mean it isn't happening.)
So in any event, if you haven't done so, you should try and communicate the problem directly to PBase staff, though I am aware that is not as certain a process as it should be.
There was a major change in the PBase back end image server setup in February last year that vastly improved performance but had a few things broken for a while, however I'm under the impression all that has been fixed.
Anyway, if you have access to a photo editor you might pass some of the problematic files through that and upload them to a temporary gallery and see if it works better. I don't think I would recommend running out and buying an editor if you have been getting by without one, but I myself feel much better having a generic process to handle my pictures.
Anyway, good luck with it -- there must be an answer.
DaveT