Dear Jason, thanks for your answer. Here are some more details on the issue:
I would like to use my iPhone 5S (iOS 8.3 (12F70)) as a hotspot for my Asus UX32LA Notebook (Windows 8.1). Both devices detect each other via WLAN and the iPhone's name is shown under the internet connectivity symbol on the Asus. As soon as I am trying to start an internet session (Mozilla firefox) the connectivity symbol shows a yellow triangel with an exclamation point, meaning that there is only a limited connection (no internet access possible). I talked to my provider (Vodaphone) already and they told me that my contract allows hotspot use without limitations.
I have tried my neighbors iPhone 5 and it also did not work.
In the meantime I have heard so many different "solutions" but none of them worked (e.g. 128-bit-encryption is not supported by the phone; Apple is blocking actively the connection with a Windows-driven device; etc.).
As I am not a computer specialist at all, I am loosing the fun of using the stuff entirely. If you need more details to narrow down the issue, please let me know but also tell me how/where to find the necessary data.
I am thanking you very much for support.
Regards,
Christoph