Take care so much, this is Arch Linux configuration, not other. See the arch phppgadmin wiki for know where are fpm.socket, it's very important! Really, really, really importante create the log files.

nginx-phpfpm-phppgadmin configuration

#user html;
worker_processes  1;

#error_log  logs/error.log;
#error_log  logs/error.log  notice;
#error_log  logs/error.log  info;

#pid        logs/nginx.pid;


events {
    worker_connections  1024;
}


http {
    include       mime.types;
    default_type  application/octet-stream;

    #log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
    #                  '$status $body_bytes_sent "$http_referer" '
    #                  '"$http_user_agent" "$http_x_forwarded_for"';

    #access_log  logs/access.log  main;

    sendfile        on;
    #tcp_nopush     on;

    #keepalive_timeout  0;
    keepalive_timeout  65;

    gzip  on;

    server {
        listen       80;
        server_name  localhost;


        access_log      /srv/http/www/logs/nginx/access.log;
        error_log       /srv/http/www/logs/nginx/error.log;

        #charset koi8-r;

        #access_log  logs/host.access.log  main;

        location / {
            root   /usr/share/nginx/html;
            index  index.html index.htm;
        }

        #error_page  404              /404.html;

        # redirect server error pages to the static page /50x.html
        #
        error_page   500 502 503 504  /50x.html;
        location = /50x.html {
            root   /usr/share/nginx/html;
        }

        # proxy the PHP scripts to Apache listening on 127.0.0.1:80
        #
        #location ~ \.php$ {
        #    proxy_pass   http://127.0.0.1;
        #}

        # pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
        #
        #location ~ \.php$ {
        #    root           html;
        #    fastcgi_pass   127.0.0.1:9000;
        #    fastcgi_index  index.php;
        #    fastcgi_param  SCRIPT_FILENAME  /scripts$fastcgi_script_name;
        #    include        fastcgi_params;
        #}

	location ~ \.php$ {
	      fastcgi_pass   unix:/var/run/php-fpm/php-fpm.sock;
	      fastcgi_index  index.php;
	      fastcgi_param  SCRIPT_FILENAME  /scripts$fastcgi_script_name;
	      root   /srv/http;
	      include        fastcgi.conf;
	 }
 
	# PHPpgAdmin
	location /phppgadmin {
		root /srv/http;
		index index.php index.html index.htm;
 
		location ~ ^/phppgadmin/(.+\.php)$ {
			try_files $uri =404;
			root /srv/http;
			fastcgi_pass unix:/var/run/php-fpm/php-fpm.sock;
			fastcgi_index index.php;
			fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
			include /etc/nginx/fastcgi_params;
		}
 
		location ~* ^/phppgadmin/(.+\.(jpg|jpeg|gif|css|png|js|ico|html|xml|txt))$ {
			root /srv/http;
		}
	}

	location /phpPGAdmin {
		rewrite ^/* /phppgadmin last;
	}

        # deny access to .htaccess files, if Apache's document root
        # concurs with nginx's one
        
        location ~ /\.ht {
            deny  all;
        }
    }


    # another virtual host using mix of IP-, name-, and port-based configuration
    #
    #server {
    #    listen       8000;
    #    listen       somename:8080;
    #    server_name  somename  alias  another.alias;

    #    location / {
    #        root   html;
    #        index  index.html index.htm;
    #    }
    #}


    # HTTPS server
    #
    #server {
    #    listen       443 ssl;
    #    server_name  localhost;

    #    ssl_certificate      cert.pem;
    #    ssl_certificate_key  cert.key;

    #    ssl_session_cache    shared:SSL:1m;
    #    ssl_session_timeout  5m;

    #    ssl_ciphers  HIGH:!aNULL:!MD5;
    #    ssl_prefer_server_ciphers  on;

    #    location / {
    #        root   html;
    #        index  index.html index.htm;
    #    }
    #}

}

Do this for configure it:
sudo ln -s /usr/share/webapps/phppgadmin /srv/http/phppgadmin
sudo mkdir -p /srv/http/www/logs/nginx/
sudo touch /srv/http/www/logs/nginx/access.log
sudo touch /srv/http/www/logs/nginx/error.log
sudo gedit /etc/nginx/nginx.conf
sudo systemctl enable nginx
sudo systemctl enable php-fpm
sudo systemctl restart nginx
sudo systemctl restart php-fpm
sudo -i -u postgres
initdb --locale en_US.UTF-8 -E UTF8 -D '/var/lib/postgres/data'
exit
sudo systemctl start postgresql
sudo systemctl enable postgresql

If you need more .information please see:
https://wiki.archlinux.org/index.php/PhpPgAdmin
https://wiki.archlinux.org/index.php/PostgreSQL
https://www.digitalocean.com/community/tutorials/how-to-install-lemp-nginx-mysql-php-stack-on-arch-linux
https://gist.github.com/maciejkowalski/5841435