No.763
Buy some stainless steel mesh off ebay.
Get 2 types of fabric, one for outer one for Inner.
Layer like and stitch like pic related.
When stitching make sure to not penetrate all 6 layers for the opening, instead do that separately.
Once done turn it inside out and there you have your pocket faraday cage.
You could just make an extra long sleeve without a flap for simplicity sake, it might even be a better idea as it leaves no chance for gaps.
Hems might be a good idea, some kind of edging to prettify the entrance, folding the edges will work as well. just make sure you fold it on the outside so when you flip it inside out you get the fold on the inside.
Easy as soykaf, only problem will be using a sewing machine, Grandma's are a safe bet in my country, maybe your school if you're still that young.
If not a steady hand can do it reasonably well, since the stitching is hidden you only have to care about it being strong, not looking good.