If you install an other version of PHP than the one provided with the distro this could, I think, have the potential of destroying any web server installation. After 7-8 years with e-smith / sme server, (or something like this) I think I have never had a serious error like this, exept for due to my own unauthorized modifications. Replacing the PHP version is that kind of modification that I would expect could lead to serious problems. (But because of this expectation I have not really tried to upgrade PHP, on SME 7.3, to see that it really did not work.)
If other users have the experience that PHP can easily be upgraded, please leave some info.
To see if the httpd-admin service is running at all: ps -aux | grep httpd-admin