Hi there,
I’m Cherrelyn, and I’m here to help.
If your sent emails appear only on your iPhone but not in Outlook on the web or desktop, it's likely that your iPhone is set to save sent items locally or to a different folder. To fix this, go to Settings > Mail > Accounts > [Your Outlook Account] > Account > Advanced, and make sure “Sent Mailbox” is set to the server’s Sent folder usually labeled as “Sent” under “On the Server”. Once that’s set correctly, future sent emails should sync across all devices. For existing ones, you may need to manually move them to the server’s Sent folder.
I hope this helps, and if you have any questions, feel free to reply to this post.
Warm regards,
Cherrelyn