This question was closed on ServerFault, as it's about a home network and not a professional-capacity one.
Is it suitable for SuperUser?
I got conflicting advice when I asked on this thread.
Our FAQ states:
not about […] smart phones, except insofar as they interface with your computer
As this seems to be an issue with your iPhone only, I'd suggest you post this question on Ask Different.
You might want to give additional details of your router's setup and the iPhone model (and iOS version). As it stands your question is a little vague.