/phppgadmin Forbidden You don't have permission to access /phppgadmin/ on this server

In Debian 8, apache2 configurations are now in /etc/apache2/conf-available and soft-linked from /etc/apache2/conf-enabled when enabled, just like virtualhosts or modules.

The phppgadmin package in its latest version comes with a predefined configuration file:
/etc/apache2/conf-available/phppgadmin.conf

This configuration should be activated by default, but otherwise it can be activated with a2enconf phppgadmin

Your old configuration /etc/apache2/conf.d/phppgadmin should be removed as well as the mentioned addition in /etc/apache2/sites-enabled/000-default.conf.

Then edit phppgadmin.conf and remove the Require local directive that you don't want if you previously had Allow from all.

you can easily solve this problem by replacing Require local directive to Allow from all in configuration file /etc/apache2/conf-available/phppgadmin.conf