This is sort of spin off and “crochet by going” kinda project. I startet with the granny square and eye balled the length I needed for the front site of the phone.

No pattern really, needed. You simply make a granny square in the colours you like, Crochet a frame around it in the colour of the remaining bag colour to close up the square. Then i added two rows of double crochet on one side and on the opposite site one row of double crochet. Followed by crocheting a singe crochet row in the back side of my loops, to make a L form in my work for the base of the bag. Followed by dc all the way up, around 14 dc and 10 rows.
Measure it out on how long you need it for your phone.
Fold it together and crochet the sides together with a crochet hook size 2.0mm.

Then in the one corner I did 10 loops on a row and tightend it up to make the holding loop.

This doesn´t take long to make, I finished it of in an afternoon/day. It´s a fun small project to do.