Type aptitude to start the package manager. There you can see which applications are installed.
Use / to search for packages. Try searching for apache2 and php5 (or whatever versions you want to use). If they are installed, they should be bold and have an i in front of them. If they are not installed (p in front of the line) and you want to install them (and you have root permissions), use + to select them and then g (twice) to install it.
Word of warning: Before doing that, it might be wise to have a quick look at some aptitude tutorial on the web.
You could inspect the available apache2 modules:
$ ls /usr/lib/apache2/modules/
Or try to enable the php module, if you have the appropriate access:
$ a2enmod
Which module would you like to enable?
Your choices are: actions alias asis ...
... php5 proxy_ajp proxy_balancer proxy_connect ..
Try this.
dpkg -s apache2 | grep Status
dpkg -s php5 | grep Status
Another way to find out if a program is installed is by using the which command. It will show the path of the program you're searching for. For example if when your searching for apache you can use the following command:
$ which apache2ctl
/usr/sbin/apache2ctl
And if you searching for PHP try this:
$ which php
/usr/bin/php
If the which command doesn't give any result it means the software is not installed (or is not in the current $PATH):
$ which php
$
How to tell on Ubuntu if apache2 is running:
sudo service apache2 status
/etc/init.d/apache2 status
ps aux | grep apache
Source: Stackoverflow.com