When using Dietpi Operating System, phpMyAdmin is one of the components which can be installed using dietpi-software framework.
Alternatively, what follows can be used:
sudo apt-get update
sudo apt-get upgrade
sudo apt-get install phpmyadmin
Select the Webserver

Configuring phpMyAdmin

Define a password for user phpMyAdmin. Preferably, should be different from root password for security reasons.
Then, create a user for phpMyAdmin, as root user cannot be a phpMyAdmin user.
Create a user and permit it to access all databases on the MySQL server by running the following command:
mysql -uroot -ppassword
use mysql;
CREATE USER username@'localhost' IDENTIFIED BY 'password';
GRANT ALL PRIVILEGES ON *.* TO 'username'@'localhost' IDENTIFIED BY 'password' WITH GRANT OPTION;
FLUSH PRIVILEGES;
Close mysql.
Apache2 configuration for phpMyAdmin
Open Apache2 configuration file and add what follows at the end of the file.
sudo nano /etc/apache2/apache2.conf
add:
Include /etc/phpmyadmin/apache.conf
CTRL+x – Y. Close and Save the file. And restart apache2.
sudo service apache2 restart
phpMyAdmin webpage is available at
“192.168.86.160:88/phpmyadmin/index.php” in a web-browser

In case a lot of errors are generated while browsing the contents of databases, apply the following modification:
inside /etc/phpmyadmin/config.inc.php file insert the following:
$cfg['SendErrorReports'] = 'never';
To extend the time-out before which phpMyAdmin will logout:
Home->Settings->Features and modify Log Cookies Validity