W samej dokumentacji php-a masz napisane m. in.
What is PHP?
What distinguishes PHP from something like client-side JavaScript is that the code is executed on the server, generating HTML which is then sent to the client. The client would receive the results of running that script, but would not know what the underlying code was. You can even configure your web server to process all your HTML files with PHP, and then there's really no way that users can tell what you have up your sleeve.
jak myślisz
Znam już mniej więcej HTML i CSS i chcę pójść w kolejny język
można by powiedzieć, żeby uczyć się obu równolegle, i tak, i nie, bo "idąc" tylko w javascript masz "duże" podstawy pod Node.js, więc ostateczny wybór należy do ciebie.
BTW, Node.JS vs PHP in 2022: Which One to choose for your project?
JavaScript and PHP are both the largest programming languages in the world with 67.7% and 26.2% respectively. Before Node.JS came around, JavaScript was no competition to PHP and was used solely for frontend development. In fact, the languages worked in tandem: JavaScript was a technology for building frontend and PHP was used for the server-side. What has changed?