PHP is not trendy but it's reliable. I see people coming back from more "trendy" things, sometimes because of the technology, sometimes because of HR problems. Probably the best answer on the subject:

medium.com/fuzz/php-a0d0b1d365d8

PHP has greatly improved in recent years, especially - performance in PHP7. I'd recommend you to take a look at Laravel framework. With Laracasts you can learn the basics of PHP/Laravel in just few weeks.

Learn any language which interests you and suits you professionally. PHP is still as relevant as it was 5-10 years back. Majority of the websites still run on PHP. Facebook didn't ditch PHP for Node Js / Go Lang. They've scaled with PHP still being part. You can always incorporate other technologies along with PHP to achieve your task.

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).

You should be interest in Backend not in programming language . So i recommend to you learn NodeJs .Because you also have javascript language. You can learn it easily. If you face any problem you can ask at Hashnode. I believe you will get the answer.

It's always good to learn something new. PHP its still the most popular backend language of web programming.