Currently you don't see much vanilla PHP, you instead see frameworks such as Laravel and that changes things quite a bit, because most of the work is done for you, and proven since in the case of Laravel it's already in version 5.4 and it's trusted by a big community, it's not something that was 'born' yesterday.
If you're purely thinking on Backend, it quite depends on your goal. If you're doing it for fun Golang is taking the spotlight, everyone is turning to it, and according to articles I've read the popularity is only going to go up.
Nodejs on the other hand, as well as JavaScript in general, is being bashed in the head by people saying how bad it is, yadda yadda yadda, they say the same about PHP, and then you just pick a language and there will be supporters and haters.
Nodejs would help you in front-end as it's more javascript, you'll learn pretty cool things, but at the same time having the same language in front and backend is in my opinion bad as you just get used to thinking the same way, in the same language, and the world as it is doesn't favor that as much.
Say you're looking for a job, my personal experience is "you have to know a bit about everything" because eventually, this again is my experience, you'll have to tackle different things.
So...
tl;dr: If for fun I would lean towards Golang, if professionally I'd go towards Nodejs (if I wanted to get deeper into JS and just work with one language), but if I wanted to check PHP again I'd turn to Laravel (given it's popularity and quite honestly from personal experience is a really good framework).