I'm still new to using Premiere, but I decided to use it to make a video for an upcoming project. I filmed on my iPhone 8 Plus and used that footage to make the video. At the end of it all, I went to export the video and it came out with these thick black borders on all sides. I'm not sure of what to do to resolve the problem?
It seems that the sequence does not fit the video.
Try the following:
In the project panel where the clip is located, right click on the clip and select, New Sequence From Clip.
Did you scale your footage when you were editing it to the timeline?
For future notice to anyone else who reads this, this definitely works as a solution. It may look like you created a new video, and in a sense, that is what you did, However, something that you may have noticed is that the video is now resized for a better export.