WP Master

It means that your host is only indexing .htm and not .php, it’s a Directory Index related issue.

Here’s the list normally recommended:

Solution 1
If allowed by your host, putting this in an .htaccess file will solve the problem:
DirectoryIndex index.html index.htm index.php

Solution 2
Some hosts allow you to make a change, via their hosting control panel, to the DirectoryIndex. It’s typically described as Indexes or Index documents, but may also require you to type something like
DirectoryIndex index.html index.htm index.php
or specify index.php as an index type file.

Solution 3
Instruct Apache to treat index.php as an index file. If you own the server, or have access to the http.conf file, simply modify the DirectoryIndex line in httpd.conf to:
DirectoryIndex index.html index.htm index.php

Solution 4
Contact your host

Did you checked your Directory Index settings? Make one file index.htm inside the root and then try to reopen your web url, if a blank page appears then there is a problem with Directory Index settings of your server.
That’s my guess.

Do you have index.php in that list?