PHP not working after 1-click LAMP Install

I used the 1-click LAMP install when setting up my droplet, and I uploaded an index.html page with some very basic PHP, just a variable and an echo. Nothing echoes out, I go and check with Inspect Element to see if the PHP code is just sitting there, and I see <!--?php $php = "php"; echo "testing ".$php."..."; ?--> instead of echoed text. Do I have to do something to get PHP to work with the 1-click LAMP stack? After all, the P [among other things] stands for PHP.