Using Outlook for iOS in business environments for email and scheduling
Same problem here, but for those of us that do NOT want to lose all our sent mail on our phones:
The best / easiest way I've found is to go into that "Sent" folder on your iphone, Tap and hold on one message to "Select" it and you will see an option at the top of the screen to "Select All".... Once you do that MOVE THEM to a folder that DOES sync with your IMAP account properly (for me I created a "iOS Sent" folder). Then on the computer move them to the correct sent items folder.
This stinks and I wish they would fix it, hopefully soon!
Best,
Mark