After difficulties via WLAN I installed pocket on an iPhone 5s directly via open internet without any problem. Works perfectly.

Hello and good day Libra222. Thank you for reaching out DJI Forum and thank you for sharing your experience. Actually, there is a possibility that the  iPhone 5s  will work on the DJI Osmo Pocket. However, since it's not yet optimized with our application ( DJI Mimo )  we cannot guaranteed the stability of the application if this will work all the time while using the specific device. We highly suggest you use the recommended mobile device that was listed on our website to avoid any problem. For reference I will post the list of recommended mobile device for the DJI Osmo Pocket. Thank you.