Install phpmyadmin

sudo apt install phpmyadmin php-mbstring php-mysql
cd /usr/share/phpmyadmin
cp config.sample.inc.php config.inc.php
cd /var/www/html
sudo ln -s /usr/share/phpmyadmin

Configure mysql

• There are 2 ways to solve this:
  1.You can set the root user to use the mysql_native_password plugin

$ sudo mysql -u root # I had to use "sudo" since is new installation
mysql> USE mysql;
mysql> UPDATE user SET plugin='mysql_native_password' WHERE User='root';
mysql> FLUSH PRIVILEGES;
mysql> exit;

2.You can create a new db_user with you system_user (recommended)

$ sudo mysql -u root # I had to use "sudo" since is new installation
mysql> USE mysql;
//If you want to access from outer network using % instead of localhost
mysql> CREATE USER 'YOUR_SYSTEM_USER'@'localhost' IDENTIFIED BY 'Password';
mysql> GRANT ALL PRIVILEGES ON *.* TO 'YOUR_SYSTEM_USER'@'localhost';
mysql> UPDATE user SET plugin='auth_socket' WHERE User='YOUR_SYSTEM_USER';
mysql> FLUSH PRIVILEGES;
mysql> exit;

Restart apache2 and mysql

/etc/init.d/apache2 restart
/etc/init.d/mysql restart