Can you place a .txt or .html file there and try to access? What would happen?
You’ll need to check the apache command line, run
ps lmax |grep httpd
for any -f key that may override the default config file location. Then check the config file for the apache home directory, it may not be /var/www
With PHP not working you should not be getting a 404 error. I would expect a PHP file to be served as plain text instead. 404 may mean Apache is using a different directory.