I'm not really sure why you would want to delay loading your index.php file by going to an index.html splash page with auto redirect to the index.php, but you may have your reason.
You can do the meta redirect in the index.html page and have it show your loading text or icon on a delay, say 5 seconds.
<META HTTP-EQUIV="refresh" CONTENT="5;URL=the-other-page.html">
Or, if you simply want the index.php to display before the index.html, then set the following code in your .htaccess file:
DirectoryIndex index.php index.html
This makes the webserver look for the index.php file first, and then index.html if it the php file is not present.