gmbs Issabel 2.5 will be provided for support/compatibility for now. New work will be done torwards version 4 (or perhaps 5). Version 4 can be installed via netinstall now, and seems to work fine with this php version:
PHP 5.4.16 (cli) (built: Nov 6 2016 00:29:02)
The default in Centos 7 I think. Not sure if it is worth upgrading php on older Centos? What is the reason to continue using 2.5 in your case? Are there any software that is not working on 4?