There was another post just like this but the OP did not post how to resolve the issue. I just updated a slew of around 100 packages through Virtualman (ubuntu box). Now all of my php pages are downloaded instead of displayed.
Apache stops and starts without issue.
root@75-145-52-45-Nashville:/etc/init.d# dpkg -l 'php5-*'
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Installed/Config-f/Unpacked/Failed-cfg/Half-inst/t-aWait/T-pend
|/ Err?=(none)/Hold/Reinst-required/X=both-problems (Status,Err: uppercase=bad)
||/ Name Version Description
+++-============================-============================-========================================================================
ii php5-cgi 5.2.4-2ubuntu5.17 server-side, HTML-embedded scripting language (CGI binary)
ii php5-cli 5.2.4-2ubuntu5.17 command-line interpreter for the php5 scripting language
ii php5-common 5.2.4-2ubuntu5.17 Common files for packages built from the php5 source
un php5-dev (no description available)
ii php5-gd 5.2.4-2ubuntu5.17 GD module for php5
un php5-json (no description available)
ii php5-mcrypt 5.2.3-0ubuntu1 MCrypt module for php5
ii php5-mysql 5.2.4-2ubuntu5.17 MySQL module for php5
un php5-mysqli (no description available)