For the first time, I was able to upload a file from my Android phone to my website server using FTP. So, I recommend this free program to anyone who would like to do the same.

AndFTP

I downloaded it through the Google Playstore. It has a small advertisement on the bottom of the screen, which I do not like, but the file transfer works. At first, AndFTP would not show me any of the files available on my phone. To fix that, I went to the Android app settings for AndFTP and changed the permissions that Android gives the app so it could access the files for uploading.

I was able to upload a big video file to my web server.

One advantage: no Wi-Fi hotspot data is used. The upload was done using the cell phone's unlimited data plan.