PHP is absolutely relevant, I'd think, by many peoples' measurements. But... we're on a 'hacker' site and people love to dump on PHP. PHP powers a large portion of internet sites. One estimate from w3techs is ~80% of sites with a known server side language are PHP.
Yes, much is WordPress. If you estimate that half of that is Wordpress, that still would leave... ~35%-40% of sites using PHP. Maybe even that is too high. What if it's 30%? That's a large number, both in terms of percent and absolute numbers.
Yes, PHP is 'relevant'. The ecosystems (Symfony, Laravel, etc) are pragmatically iterating, evolving goods ideas from a wide spectrum of web platforms. The language itself is similarly pragmatic, adopting new features, deprecating legacy stuff, and moving forward. The language is roughly 3x faster than it was 10 years ago, while retaining a lot of backwards compatibility.
The language itself along with various frameworks offers a good combination of speed of development, flexibility and rigor. The 'shared nothing' default makes it easier to reason about for many problems. Need to write a small shell script? Easy in PHP. Need to scale up to large loads? PHP can do it. There will be scaling concerns in any large setup - a PHP platform will likely have similar problems that other language/stacks will encounter at similar load.
So again, yes, it's relevant. There will be some other response saying "no", and then ... we'd have to define what you mean by 'relevant'... :)
Popular? Growing? Evolving? Uptick in usage for many problem spaces? Easy to scale?
I'd say 'yes' to all of those.