Even if you are just talking about clean code for your own satisfaction whether or not a single PHP file is "clean" or not (to me) depends heavily on the comple

Even if you are just talking about clean code for your own satisfaction whether or not a single PHP file is "clean" or not (to me) depends heavily on the complexity of the application. If your service only needs 50 lines of business logic, a single PHP file probably would be easier to understand and maintain than modularizing it. (I have no idea how many lines of code remoteok needs).