Hello,
create file e.g. "info.php" and insert following lines:
<?php
echo phpversion();
phpinfo();
?>
Put this file to the same folder where install.php is located.
Point your browser to http://ocsinventory-ng/ocsreports/info.php and check result.
Do you see version 5.6.30?
OCS uses the same function (phpversion();) for PHP version detection.