I made this for my daughter for Christmas. I had to sneak her cell phone away from her to make sure the sling would fit her phone exactly, and she had no clue! She absolutely loves it!
I made it with a thin (single crocheted) strap, designed to wear over the head and hanging at your hip on your side.
The main holder was double stitched (crocheted). I hot glued the patch on, squishing it on there until I could feel the hot glue coming through the thin gaps and attaching itself to the yarn. Make sure you separate the front from the back so the glue doesn't stick both sides closed.
I attached the charm and chain with a jump ring around several strands of yarn to ensure it stays in place.