Решавам проблема, като въвеждам реда:
Require local
в phppgadmin.conf:
# Fichier phppgadmin.conf
Alias /phppgadmin "C:/wamp/apps/phppgadmin5.1/"
<Directory "C:/wamp/apps/phppgadmin5.1/">
Options Indexes FollowSymLinks MultiViews
AllowOverride all
Require local
Order Deny,Allow
Allow from all
</Directory>