I created the fabric sizes and showed the general steps for creating the pouch in Sketchup.  French seams is the key for the sides to make clean, finished edges.  If a slightly different size is needed, use the dimensions shown and adjust the "green" sections to fit your particular needs.  I had done an earlier version that was a little too small and just added 1/2" to the width as shown here and worked well for an iPhone XR.