Right tool for the right job. You can use qualifiers like "serious" and "modern" but you're deluding yourself if you think they mean anything when the pool of PHP developers is so staggeringly high.
Of course, right tool for the right job. PHP has specific use cases but that's another discussion entirely.
Ive also seen much worse in Java world, with JSPs and all kinds of taglibs and action-handlers mashed up to create a soup which would make you crave for PHP.
People here love to poke fun at WordPress. I'd love to take any of them out of startup-land and make them work for a full week in a 10 years old corporate piece of software, written pretty much in any language.
A "serious PHP developer" is an oxymoron.