This is true, and I wouldn't turn my nose up at a job from a company I really like (eg. MailChimp) just because it was PHP.
However as far as professional development concerned, I'd be very concerned about being hobbled by sticking with PHP over the long term.
First, because it doesn't have any strong ideas to explore as a language, it just cobbles together ideas from other languages in a very ad-hoc and half-baked manner. If you want to learn the power of first-class functions with closures for instance, those things exist in PHP, but the syntax is so baroque that you'd be excused for thinking they're not worth the trouble.
This effect is compounded by the fact that the PHP community is an archipelago of experts in a sea of beginners. If you're a newbie coming in it's relatively hard to figure out who to listen to to advance your skills.
Finally, there's the external signaling aspect. Although it's unfair, the hard truth is that software developer talent is the classic market for lemons. Most people evaluating you will not have the knowledge and experience to evaluate your skills objectively (heck, I'm a hiring tech lead and even I can't really tell until I actually start working with someone). For a lot of people, the language you use is the signal they use, and in this regard PHP is at the bottom of the food chain just about HTML/CSS.