Well, since PHP is run on the server while JavaScript is run the client (the browser) - at least if we assume we're discussing a typical web application here - then there is no real corollary to JavaScript's prompt() function.
You could do something similar perhaps with an AJAX implementation. In fact, you could acutally use the JavaScript prompt() function as part of that implementation. But without knowing exactly what it is you want to do, I can't really say if that or something else would a better solution for you.