Here's a little, super easy, super quick DIY for you.
This is one of those spontaneous projects that I started without really having a plan beforehand, but which surprisingly turned out pretty OK!
What you'll need is a rectangular piece of leather, in which your phone will fit, leave a little space at the top.
Fold the two upper parts to create a hem and put some stitches on each side of the rectangle. Cut off excess leather.
Make a little incision with a stanley knife through the top of the leather or use a paper perforator to make a circular hole.
Put a necklace(I used a thrifted one I never wear) or a chain through it and you're done.