Once your strip is cut, lay flat on the table. Turn down the top of either side about 1 inch all the way around the strip.
If you have trouble with this, try doing it in stages by spinning the strip around.
Put some fabric glue along the turned down piece and fold up the shirt to glue together.
Be sure to leave spaces with no glue (~4-5 inches), so you can slip your phone and other accessories into it!