Post your videos and pics as either square or vertical on Facebook.
Then your posts will take up the whole phone screen instead of just 1/4 of the screen, which is what you get in the landscape.
If you’re on Facebook, scroll through your feed to see if this is true.
Then consider how much more effective your posts will be, especially if you boost them.
See this picture below, if you’re on your phone. Is it full-screen or just 1/4 of your screen?