Print the STL file that contains the entire object (all of the separate parts combined into one). Print the object laying flat with the rotary dial facing upward. Use support and brim to prevent warping. If your printer has a standard 0.4mm nozzle, change the Extrusion Width in your slicer to 0.3mm to be able to print the embossed numbers. If you are using Simplify 3D as your slicer, be sure to use the Mesh/Separate Connected Surfaces function prior to slicing. This will ensure the separate parts will be sliced as one object (yes, it's counter-intuitive, but it works). Use 0.1mm or 0.15mm layer height. Use a moderate support density to make it easier to remove the support. Since the supported area will be hidden when the phone is installed, any decrease in surface quality due to this setting will not be noticeable.