So far I have not personally run into anything I _can't_ do in PHP - it may take some creative thinking, but there is usually a solution - this includes "advanced" functionality as well.
I think what a lot of the issues people have with PHP is not that it can't do something, but more that many of the ways you implement something feels like a "hack" - it works, but isn't as elegant as other languages.
I wish they would have put more effort into deprecation and cleaning up past messes instead of building new features to attract serious developers and making things even more of a mess.
PHP is trying really hard (it seems) to be a more advanced language, possibly to get new users to move over from other languages.
But they don't need to.
They should just stick to their roots, do what they do best:
Super small learning curve, low barrier to entry, it's everywhere, it works great for most apps, keep CRUD super-simple.