Webtatic has now ended support for PHP 5.5, and suggests either:

• Upgrade RHEL/CentOS to 7.2, so that you can install php 5.4.16, which is still supported by those distributions.
• Upgrade PHP to the one of the latest available versions, which Webtatic supplies PHP 5.6 for EL6/EL7 and PHP 7.0 for EL6/EL7