PHP directives are PHP options that are usually configured in php.ini files. You can consult the list of PHP directives here https://www.php.net/manual/en/ini.list.php
On DirectAdmin servers, the php.ini files are located in /usr/local/phpXX/lib/php.ini where XX is the PHP version. For example, for PHP 7.2 the file will be /usr/local/php72/lib/php.ini . Many times, you might need to check a directive for all PHP versions. To do so, you can use this command:
grep directive_name /usr/local/php*/lib/php.ini
Example:
grep memory_limit /usr/local/php*/lib/php.ini
On a test server, the output is:
[root@web custombuild]# grep memory_limit /usr/local/php*/lib/php.ini
/usr/local/php70/lib/php.ini:memory_limit = 256M
/usr/local/php72/lib/php.ini:memory_limit = 128M
/usr/local/php74/lib/php.ini:memory_limit = 192M
/usr/local/php80/lib/php.ini:memory_limit = 128M
[root@web custombuild]#As you can see, you can easily check the value for a directive (memory_limit in our case) for all PHP versions installed on the system.