Since I want to 3d print an enclosure for it I was wondering what the most efficient way of getting rid of this interference is ?
Installing it inside a box with aluminum foil on the inside?
Should connect the foil to ground?
Will the holes that I need to make in the box for the buttons and leds not cause any leakage?
You are on the right track, one solution for you would be to make a Faraday cage. This is what you are thinking about, I think.
Loosely speaking: It's essentially a conductive shield enclosing your apparatus. If you do decide that you want some holes through your shield, then that's fine because the wavelength of the RF waves that the cell phones are using are in the MHz range (I believe), which have wavelength's of several centimeters. This means that for them to pass through the hole, the holes need to be at least a quarter of the wavelength in diameter to pass it through. I am not 100% sure about the quarter wavelength part though... so someone will probably correct me
And yes, connecting it to ground will allow any currents that comes from noise to dissipate safely through ground, instead of your signal traces.
Install it inside a box with aluminum foil around it that is connected to ground. Make some small holes for wires to pass through, the smaller the holes the better.
The leakage will most likely not be noticeable due to the wavelength's of the RF waves that the cell phones are using.