You won’t find anything that will be able to import from static pages to WordPress, I am reasonably certain of that.
Are the PHP pages mostly of the same format (ie: Header, Footer, Sidebar(s) and a section for Content)?
If so, you could find a WordPress Theme that you like (or start with one of the free ones, Twenty Fourteen is pretty good). Format this so it suits your needs, then create pages/posts for each of the old static ones by pasting in the “Content” from each page into WordPress.
It’s not perfect, and it’s simpler if that content doesn’t contain PHP or images.
That ought to get you the posts/pages in WordPress, albeit a LOT of work, and from there you can edit each, converting images etc to be in the regular WordPress Media folders, and then update/change theme so the site looks how you want it to.
The other factor is SEO/Duplicate content, since Google could penalise you for duplicating pages. I would recommend setting the new site to not get indexed until you are ready to do that, and of course the pages are almost certain to have a new url. You could create redirects in your .htaccess file so the old pages are redirected to the new ones, or make sure the WordPress pages have the same url as the old (nice if you can manage it, but WordPress pages don’t end in “.php”. You could strip this in the redirect though).
Hope this helps in some way.
