Per https://www.php.net/manual/en/function.ldap-connect.php the signature $conn = @ldap_connect($host, $this->port); is deprecated since PHP 8.3.
Thus pass a full LDAP URI as the only parameter.

ERROR 8192: Usage of ldap_connect with two arguments is deprecated at [/var/www/html/phorge/phorge/src/applications/auth/adapter/PhutilLDAPAuthAdapter.php:308]

Closes T15724

Set up LDAP as auth provider, try to log in.