How to start PHP localhost in the command line and then run npm build?

I’ve been trying to deploy a react app, was messing around for a while until I realized you have to build it on the component settings, but I also want to build a PHP server to manage some queries, when I do it on my machine I open a terminal and run PHP -S localhost:8000 them I head back to the root folder and run npm run build and it works. Tried the same workflow on the DigitalOcean panel but it’s just building the app without the server

I know I’m probably missing something in the workflow but what I have in the commands tab is

cd PHP/
PHP -S localhost:8000
cd -
npm run build

is there any way to run both commands at the same time and how do I know on which port is the build running?