100 % is difficult, but as far as I know, this is completely unimportant.
HTML pages in most cases are static and not dynamically "produced", so they are faster to read than php pages. This would have a positive effect on ranking in SE.
But if You rename through htaccess or somehow the php pages into html, it does not make them static, so I think this is a big error to think this would help on SEO.
If You can cache Your php sites on Your server, than they are as fast as static pages, and they rank the same i would say.
You may check any search term and compare the first results if You find more html pages or php pages. Just choose a very popular search term, where You can be sure that these sites are heavily optimized.