You will need:
2 cell phones (one to test with and one that causes interfernce)
1 9 inch piece of foil (tear off 9 inchs of foil)
a flat surface to fold foil.
Parental Guidance if needed.
Step 1: Folding the foil
Place your phone on top of the foil, near the top edge.
Now fold the foil in the middle by bringing the bottom of the foil over the phone. Meet the two jagged edges together and crease the new bottom edge.
See diagram (fold on red dotted line)