You need to run yum in order to use PHP after setup your CentOS 8. Even though you have httpd, PHP may need to be installed manually.
First of all, you need to check if you have httpd on your CentOS 8 server as following:
ls /usr/sbin/httpd
If it does not exist, you can install it simple as following:
yum -y install httpd
If everything is okay, please run below commands to install PHP packages you need.
yum update yum install php php-common php-devel php-bcmath php-gd php-pdo php-pear php-mysqlnd php-mbstring php-xml php-tidy php-soap php-pecl-apcu php-pecl-ssh2 php-mcrypt php-pecl-memcache php-intl php-zip redis ImageMagick-devel
If you face following errors,
No match for argument: php-tidy │ 819 root 20 0 93516 9564 8504 S 0.0 0.1 0:14.74 /usr/lib/systemd/systemd-journald No match for argument: php-pecl-ssh2 │ 1308 root 20 0 95304 9584 7372 S 0.0 0.1 0:13.01 /usr/lib/systemd/systemd-logind No match for argument: php-mcrypt │ 2140 root 20 0 98M 6668 5724 S 0.0 0.1 0:00.69 /var/lib/pcp/pmdas/root/pmdaroot No match for argument: php-pecl-memcache