This is how I managed to have PHP 5.6 on a fresh CentOS 7.

yum install epel-release
rpm -Uvh https://mirror.webtatic.com/yum/el7/webtatic-release.rpm
yum clean
yum update

Then…

yum install php56w php56w-opcache php56w-mcrypt php56w-pdo php56w-mysql php56w-mbstring php56w-gd php56w-dom

ImageMagick

yum install ImageMagick php56w-imagick

Restart httpd

service httpd restart