Linux – How to enable bcmath module in PHP 7.1

The Apache functions are only available if running the httpd SAPI, also known as mod_php.

The stock CentOS PHP packages make mod_php available, so they are enough to allow them. If you need a newer version than the stock packages then you will need to find newer packages somewhere, or you will need to build PHP or the PHP packages yourself with the proper SAPI.

Assuming that you're installing a PHP module for Apache, you need to be using the same version of Apache it was built against. It's a bad idea to try to mix-and-match source packages and binary packages like this. Either find a reputable repository and install everything from there, or build everything from source, but trying to mix it up like this will usually lead to this sort of problem.