Did you install php individually or did it come in some package with apache and mysql?
I ask that because we won't know what you had in your original index.php page as it could be different depending on what you downloaded and installed.
If all you want is the phpinfo to show up in your index page then simply use a text editor and create a page named index.php and place this coding in it:
Don't put any other html in it as it will generate all of that by itself with the phpinfo function.
On another note this really belongs in the PHP forum. I'm sure someone will be along to move this.