I came across that few times in beginnings.
If you make a request to your php file, and Web browser is asking you to download it, it should be fixed and resolved at the origin host/server side.
I assume you are using Apache Web server by stating that one configuration file? If so kindly re-check MIME types at httpd for .php extension.
There has to be some misconfiguration with PHP settings/module.
Do you see anything in error.log?
Re-check CHMOD too.
What PHP version are you running?
Moreover, may I ask have you tried accesing your webpage using another web browser or clearing your web browser cache? (not the Cloudflare one)
This is something your hosting provider should resolve as far as it seems to me it is out of the scope for this forum, but maybe some ideas where to look up for to find a solution, kindly check on stackoverflow or serverfault for possible solutions.