If you are uploading photos and videos to facebook directly from your phone, you may have noticed that the quality is not on par as the photos you are uploading from your computer. The reason for this is that by default, the facebook app is set to upload low res photos and videos to facebook to save bandwidth and data charges.
If you want your photos and videos uploaded at maximum quality, here is what should should do:
On iPhone, go to facebook app settings then photo and video, and check “Upload HD” under both photos and videos.
On android, go to settings and check Upload HD photos (I did not find a setting for HD videos)