The most appropriate solution to fix this issue is to take the quarter zip fleece to a tailor or seamstress. They will be able to properly inspect the pocket and stitch it back together so that it can securely hold items. Alternatively, you could also try repairing it yourself with a needle and thread, however, you would have to be careful not to cause further damage. If you do not feel comfortable attempting this yourself, then having a professional sew your pocket back together is the best option.