what app to open php files?

A PHP file is just a regular text file. You can open it with pretty much anything. Even sometihng as simple as TextEdit on a Mac by default

But PHP files are meant to be delivered form a web server to a browser. The are Web Page files.

If you open them with a text editor all you'll see is PHP code.

Where are you getting these PHP files you need to open?

Did it just download a PHP file?

That's not correct. Must have been an issue with the Website. PHP files would not be articles. And should not be offered for download. Unless the particular website is providing some other format of file that just happens to end in php.

Do you have a direct link to this article?

Yeah, that's just an error. Seems like a transitional page. wait.php would not contain any article.

Its a website issue. You may need to contact the Website admins and tell them about it if possible.