Right, you do not want your clothing rubbing against your phone and making distracting, annoying, and possibly noises that muffle the shop conversation. I use my smartphone and put it in my shirt pocket. If necessary, depending upon the shirt I wear during the shop, I can use paper napkins or tissue and/or a clip-on ballpoint pen to make the phone fit snuggly. As a rule, my phone is generally stowed when possible during mystery shops.