I recommend one that will be tight on your waist when worn there and in a color that you don't mind wearing.
Grab your scissors and glue.
Measure a little more than twice the width of your phone up from the hem of your shirt, and cut straight across.
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!
Again, if you have trouble, try doing it little by little and spinning the strip around. Remember to leave those pockets!
Give the glue about 10 minutes to dry before trying on your new no-sew running belt.
Your phone should fit snuggly into your new running belt. Put it in with the headphone jack facing out, if you're using wired headphones.
My belt does not slip when running or jumping, and it works excellently.
Get out there and enjoy the maiden-run with your new belt!