Largely both I'd imagine. Facebook, Slack, and Etsy all still run PHP (or Hack which is a PHP flavor) as far as I know. I'm sure there are a ton of other large web properties doing the same for their web tier.
Etsy still uses PHP, as does Vimeo and Wikimedia. A few other launched-in-early-oughts web properties rely heavily on it too (e.g. Flickr).