After hours of searching I think my problem was that command yum install php-soap
installs the latest version of soap for the latest php version.
My php version was 7.027
, but latest php version is 7.2
so I had to search for the right soap version and finaly found it HERE!
yum install rh-php70-php-soap
Now php -m | grep -i soap
works, Output: soap
Do not forget to restart httpd
service.