SEO is the assessment of Words on a HTML page.
The HTML page is served up from a Server.
PHP is a language which runs on the Server, and can respond to the request for the page in a variety of ways.
For example it could serve different Words as part of the HTML output depending upon the time of day or the perceived location of the Browser requesting the HTML page and many other options.
Does serving different words to different time zones, or to different countries on the same webpage help SEO? I don't know.
Does serving different words to different countries on different webpages help SEO? I think so.
Typically in PHP each of those webpages would actually be the same single page, but the Words appearing on it would depend upon the language chosen. If you changed the order of the images, say, you'd only actually change one page (a template).
Does the PHP itself help SEO, no it does not.
Used cleverly in combination with other tools/knowledge, yes it has its part to play - but you could achieve the above by maintaining 3 different static HTML webpages.
But that would mean if you changed the order of the images, you'd have to change 3 pages.
Then imagine you were supporting more languages.