You need to run yum in order to use PHP after setup your CentOS 8.
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