Plesk Onyx 17.8 is installed.
phpPgAdmin is not available for installation in Tools & Settings > Updates and Upgrades.
phpPgAdmin is not shipped with Plesk 17.8 and it is removed from existing installations during the upgrade to Plesk 17.8.
phpPgAdmin project has been inactive for the past 3 years, which lead to phpPgAdmin becoming an insecure and unstable application.
Customers who need to edit their database using a web interface can install a stand-alone phpPgAdmin on their websites.