openssl and tokenizer php extensions are included in php-common.x86_64 package,
you have to launch this command

$ yum install php-common.x8664 php-mbstring.x8664

This question was answered by @muhammadsufiyan:

this might help you, try to run below command using putty:

yum search php-

it will show you a list of available extensions then to install you need to run below command:

sudo yum install php-extension-name-here

You can see the comment here.