PHP Safe Mode is under the domain level control panel, under Setup.
There will be the following:
PHP support [CHECKBOX] (PHP 'safe_mode' [CHECKBOX] on )
The checkboxes obviously being real check boxes. You need to first of all have PHP support enabled, and by default in PSA 8.x safe mode is enabled, just uncheck that box, which is to the right of PHP support.
You may also want to restart the webserver.
Thx
James