Question

I can’t install any php extension

Epel repository enabled

yum repolist shows

repo id                                repo name                                                                      status
base                                   CentOS-6 - Base                                                                  5,932+362
epel                                   Extra Packages for Enterprise Linux 6 - x86_64                                 5,867+1,143
extras                                 CentOS-6 - Extras                                                                        4
updates                                CentOS-6 - Updates                                                                  334+83
repolist: 12,137

yum install php-soap
or
yum –enablerepo=epel install php-soap output:

    Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
 * base: mirrors.dedipower.com
 * epel: mirror01.th.ifl.net
 * extras: mirrors.dedipower.com
 * updates: mirror.as29550.net
Setting up Install Process
No package php-soap available.
Error: Nothing to do

Answer 1

You should check your /etc/yum.conf file.
It might be that there is a line that looks something like:
exclude=php*
Wich will prevent you from installing any PHP extentions.

If youŕe using DirectAdmin, you should probably check this out:
http://woshka.com/blog/linux/centos/direct-admin-control-panel/compile-and-enable-soap-into-php-with-directadmin-controlpanel-custombuild.html