WordPress won’t install

When I try to install WordPress the wp-admin/install.php page is displayed as code. I am using MAMP on OS X (latest versions) to install on my home computer. I believe I followed the “Installing MAMP”, “Installing WordPress” and “Editing wp-config.php” instructions from the WordPress.com codex correctly. According to MAMP, Apache Server and MySQL Server have the green light and are working. If PHP is not installed and/or configured properly how do I know? What else could be the problem? Thanks!