There appears to be a few options you can investigate (one with Docker containers and one without). Personally, I would give the complexity of understanding Docker containers a miss and get started with Justin Ellingwood and Kathleen Juell's article:

• How To Serve Flask Applications with Gunicorn and Nginx on Ubuntu 18.04 by Justin Ellingwood and Kathleen Juell; or
• How To Build and Deploy a Flask Application Using Docker on Ubuntu 18.04 by Michael Okoh.

phpMyAdmin will complicate matters a little, as you will be installing PHP, purely to serve phpMyAdmin. You again have a a couple of options, and I would suggest the easiest by far is to move away from phpMyAdmin and look at a Desktop equivalent:

• TablePlus is a desktop application that I use and it works quite well;
• Otherwise, you can install MySQL and PHP by following the steps in How To Install Linux, Nginx, MySQL, PHP (LEMP stack) on Ubuntu 18.04 and then install phpMyAdmin seperately from there.

Good luck!