To install php and open lite speed in direct admin server use these commands
cd /usr/local/directadmin/custombuild
./build update
./build set webserver openlitespeed
./build set mod_ruid2 no
./build set php1_mode lsphp
./build set php1_release 5.6
./build set php2_mode lsphp
./build set php2_release 7.3
./build set php3_mode lsphp
./build set php3_release 7.4
./build openlitespeed
./build php n
./build rewrite_confs
In above mentioned commands you can use multiple php versions as php1 to php3