Our PHP Selector works with DirectAdmin only if PHP is running in suPHP or FastCGI mode. Here is the complete set of commands to enable selector on DA with suPHP:

/usr/local/directadmin/custombuild/build set php1_mode suphp
/usr/local/directadmin/custombuild/build set cloudlinux yes
/usr/local/directadmin/custombuild/build set cagefs yes
/usr/local/directadmin/custombuild/build update
/usr/local/directadmin/custombuild/build apache
/usr/local/directadmin/custombuild/build php y
/usr/local/directadmin/custombuild/build suphp
/usr/local/directadmin/custombuild/build rewrite_confs
cagefsctl --force-update
cagefsctl --remount-all

Same way for FastCGI mode.