Question: After installing LAMP you still have problem to open php pages . How to solve this issue.
First check if this packages is installed : libapache2-mod-php5 ,if not install it using this command:
sudo apt-get install libapache2-mod-php5
Now open your firefox and clear the cache and history
reboot your apache server sudo /etc/init.d/apache2 restart
Method tested and working under ubuntu and debian versions