I don't know if this is still true, but the impression I got at the time was that PHP is constantly trying to catch up with more advanced languages. There was no case I could point to and say "PHP is the best choice for this".
If I want to write a highly concurrent distributed system I'll reach for Elixir/OTP. If I want high performance, I'll reach for C or Rust. If I'm working on a data science project, I'll reach for Python or R. When is PHP the language to go to?