it's just "yet another c-style/curly brackets scripting language", which isn't hard to learn and especially easy to use and which was and still is heavily used in context of web-development.
why? its very efficient/productive ... which is of special interest for example for smaller fixed-rate projects, mvps and similar use-cases.
even if php has many flaws, it got a few things right and is for example available on nearly every webhoster out there ...
but: don't stop learning programming-languages with php. add for example javascript, but also python, some functional language - no, not haskel, i prefer ocaml - and other languages to your "selection of tools" ... :)
btw. another example ... "everybodys darling" javascript:
compared to javascript php is a pretty decent language ... just search the net on critiques on javascript, and despite that: everybody uses it.
why? because its in every browser / on every system / every mobile-platform etc.
availability/accessibility/... counts more than some academically influenced aesthetic discussions from some "theoretical computer-science point of view" ;))