Apple's mechanism is easy to use, but doesn't conform to the underlying standard and especially is a breach of your online privacy. Every site whose network you use with this configuration will know, that you are at their site at that time and could potentially attribute the network traffic you cause to you. Do not use an iPhone with this configuration if this concerns you.
To resolve this issue, you need to find a way to set an outer/anonymous identity of "firstname.lastname@example.org" and an inner identity of YOURCAMPUSNETUSERNAME@jacobs-university.de as shown in our How to configure eduroam on Android guide.
Follow Apple's guide to join a network.
In the step "Join network", select "eduroam".
In the step "verify password", you need to enter your JACOBS account in the format YOURCAMPUSNETUSERNAME@jacobs-university.de as username and your associated password.
Screenshots of the process
Select eduroam WiFi/WLAN network:
Accept the security notification about the certificate: