The original pattern calls for a 3mm needle, which I think is an American size 2 or 3. I wanted to get this done in a hurry, so I used a size 8 needle. I cast on 24 stitches and knit this as a tube. My boss's phone was a slider, about 4 3/4 inches long so I made it a little longer than the pattern calls for to fit it (5 inches). When I got to the top, I continued the k2,p2 rib but switched to a size 5 needle. You could probably use a 6 or 7 if you have it. The top ribbing with the smaller needles is about 2 inches and bind off. The top gets folded over like a cuff. I knit the pocket piece separately with a 12 stitch cast on, about two inches long, in a k2,p2 rib and sewed it to one side of the cell phone sock.