Your iPhone Is Not Uploading HD Photos And Videos To Facebook By Default
After upgrading my phone and coming over to iOS, I began uploading videos and photos to FB via the app itself only to find out that it was not uploading it in HD quality at all.
By default, your app is set to NOT upload them in HD unless you specifically turn it on. The good news is that it's really easy to do so.
Simply go into your Facebook settings, locate Videos and Photos, and then turn on the Upload HD setting for both photos and videos.
As a bonus, you can also stop videos from auto-playing here in this section!
This setting is specifically for iPhone itself. I believe Android users also must enable the setting elsewhere.