In addition to the package installation, the One-Click also:

Enables the UFW firewall to allow only SSH (port 22, rate limited), HTTP (port 80), and HTTPS (port 443), and MySQL (3306) access.
Sets the MySQL root password and runs mysql_secure_installation.
Sets the phpMyAdmin admin password.
Sets up the debian-sys-maint user in MySQL so the system’s init scripts for MySQL will work without requiring the MySQL root user password.

After you create a phpMyAdmin One-Click Droplet:

You can access phpMyAdmin immediately by visiting the Droplet’s IP address in your browser followed by /phpmyadmin.
You can log into the Droplet as root using either the password emailed to you or with an SSH key if you added one during creation.
The MySQL root password and phpMyAdmin admin password are in /root/.digitalocean_password.
You can get information about the PHP installation by logging into the Droplet and running php -i.

The default landing page, shown when you visit the Droplet’s IP address, is located at /var/www/html.
The phpMyAdmin configuration file is located at /etc/phpmyadmin/. To secure your connection, you will need a registered domain configured for your Droplet.