This is a bit of apples and oranges, as PHP is a scripting language and Joomla is a content management system (CMS). PHP is basically a Perl-like (though with significant differences) language specifically designed to integrate with HTML.
Is your website in static HTML code? If so you may wish to research the CMS offerings on the market and migrate, so that you can better control and maintain your site.
There is a great site that I’ve used many times to demo both the back- and front-ends of PHP and open source
software – called opensourcecms.com. You might wish to visit and play around to see what type of system might be to your liking. It’s a good way to try out and get a feel for using the software.