If you have just installed PHPlist and get this message, make sure that your Apache configuration has somewhere

DirectoryIndex index.php index.html

or that at least index.php is mentioned before index.html

For other webservers please consult your manual to find how to make index.php be the default document for a directory.

Alternatively you can delete the file “index.html” in the lists directory of PHPlist

You probably want to be here or here.