You can write a server that will handle multiple requests in PHP, for example, using ReactPHP.
By the way, I don't like how they implemented promises and asynchronous file streams: they copied them from Node.JS and didn't implement proper error reporting (which Node did't have at the time too if I remember correctly). For example, if there is a promise that was rejected and the rejection is not handled, there will be no exception thrown. So the developer won't even know about an error, even if it is a syntax error. That's how poorly Javascript promises were designed. Now this is fixed in JS and unhandled rejection will produce a warning in the console but there are many other bad things about them.
By the way, I don't like how they implemented promises and asynchronous file streams: they copied them from Node.JS and didn't implement proper error reporting (which Node did't have at the time too if I remember correctly). For example, if there is a promise that was rejected and the rejection is not handled, there will be no exception thrown. So the developer won't even know about an error, even if it is a syntax error. That's how poorly Javascript promises were designed. Now this is fixed in JS and unhandled rejection will produce a warning in the console but there are many other bad things about them.