Backing up your database in Phpmyadmin is accomplished by doing the following:
1) Once you have reached the PHPMyadmin screen, select the database you want to back up.
2) Select the 'export' tab on the top right of the screen.
3) Scroll down the page and click 'Save as file' and click on the 'go' button. This will save a copy of your database on your local computer.