Are there many serious companies using PHP?
It overwhelmingly seems like the language of the cheap and not very technical or providers of services to the cheap and not very technical.
It is used all over the place in ways you don't even realize. "not very technical or providers of services to the cheap and not very technical" is a particular corner of the market that is visible and full of PHP, sure, but you don't see the huge masses of PHP code running that doesn't expose a .php on the end of the URL.
It's mainly used by profitable and/or public sector orgs, so unlikely to have much intersection with the HN crowd.
Wordpress and Nextcloud are two very prominent pieces of software that come to mind that are built on PHP. I'm sure there is more out there.
Netgate (behind pfSense) use PHP for their firewall administration interface.
They recently posted about how to patch their software from the command-line (https://www.netgate.com/blog/critical-php-security-update)
Facebook (although they forked it)
Wikipedia
Wordpress
How old are you?
Isn't there some large php based software run by a bruised ego who can't even get his own house in order, let alone help fund his largesse, but complains about his leeches.
Hrmmm.
Is Facebook still using it?
Also, not a company but Wikimedia Foundation definitely has some funds too.
It's used on Pornhub so it's both very useful and very important but excuse me princess if it's not on the next Mars lander robot.