In a heat-resistant glass, add in the condensed milk (you can add more or less to your taste).
To the coffee phin filter "cup," add 2 tablespoons of coarse ground coffee.
Gently tap to ensure the coffee grounds are evenly spread out.
Place the top disc on and carefully screw it over the filter "cup" with your fingers. Use a metal spoon and continue to tighten until you feel some resistance.
Place the coffee phin over top of the glass with the condensed milk.
Pour about 1 tablespoon of hot boiling water into the coffee phin to bloom the coffee grounds and observe how quickly the water drips through. If it's dripping quickly, carefully use a spoon to tighten the filter. (Note: the coffee filter is metal so it will be hot). If no coffee is dripping through, then carefully use the spoon to loosen the filter a bit.
When the coffee is dripping at an ideal slow rate, pour the rest of the hot water (it should take about 4-5 minutes for the coffee to finish dripping through) and place the cover over top.
Add ice cubes to a tall glass.
Once the coffee has finished dripping, remove the phin filter.
Stir the condensed milk and coffee together, and pour into the glass with ice.