Although a Basic PHP Design is well pretty primitive these days, I still get request to design these types of sites. The reason being for example is some older Web Designers still want to be able to edit the code themselves but don't understand or want to learn such things as CSS. As a matter of fact I still have a client that uses Frontpage even though it's been obsolete for over a decade.
Back in the old days one would have to create different sites to accommodate this same responsive function. Imagine having to create a mini site for all the types of phones or tablets back them.
Way back when I first started Web Designing, everything was coded per page. That meant let's say you had a site with a hundred pages, well that meant I would have to go in to each page and make that change. That became a huge headache until I found out about "includes" afterwards I design all sites with includes so the owners of the sites would only have to edit the section, such as the header, left menu and footer.
However even still one has to go page per page to edit things like tables or text size and text colors.
Another way around the this though is to install a CMS ( Content Management System ) where they could edit the text and image(s) within the body of the page. It's a little cumbersome but has solved at least the body content per page for those that want it.
PRO’s OF A BASIC PHP SITE:
Easy for a beginner or old timer that want's to stick with basic HTML so they can edit themselves. Using the .php extension they would still be able to use the same page name even though the page code inside does not contain any PHP.
For starters if at a later time they want to go with CSS the would need a re-design. Each page has to be manually edited to make a change / update, except for like the header, footer, left menu. Tables and Font Sizes and Font Colors etc. have to be done page by page. Very time consuming for the beginner or old timers.