Pour condensed milk in a tall glass. Place the phin filter chamber and cup spanner on top of the glass, remove the filter and measure out the coffee, leveling it out by gently tapping the chamber. Place the filter on top, and pour just a touch of boiling water into the filter, just about to the level of the filter (about 20 mm or so) and let the water absorb into the coffee. Proceed to fill the chamber with the rest of the hot water to the top, cover, and let it steep until all the water passes through the filter. This can take some time, about 6-7 minutes.
Remove the filter, stir the condensed milk and coffee, then pour over a tall glass with ice. Serve immediately.