I know enough PHP to build basic sites and troubleshoot existing ones, like WordPress sites.
I guess it's pretty convenient that the website you're currently looking at was made from scratch using PHP. I chose PHP for this site because reusing components is simpler and less overkill than a JS-driven framework like React or Angular. Plus it's always good to brush up on it, since so many sites are built with WordPress.
The cookies disclaimer on this site required a working knowledge of how JS, PHP, HTML, and CSS all work together. It basically works like this: