iPhone drastically slowing down wifi Every time I connect my iPhone to the home wifi the connection slows down drastically. I don't have any uploads running neither system updates so I cannot understand what is causing this issue.

I have checked on the router if I can limit the bandwidth but this cannot be done. I have also tried to reset network settings without success.

The iPhone was bought in the states (I think) and I am using it with a wifi for th Italian market. Could this cause the problem?

Any suggestions appreciated.
You'll want to check the diagnostics offered by the router.

In some cases your router could be "beam forming" to maximise bandwidth to a single device (such as a laptop). If you have relatively bad conditions, this could be necessary to get good speeds. By bad conditions I mean for example neighbouring WiFis networks interfering, noise from other equipment, big distances between router and device or objects blocking the signal (walls for example).

If you add another device to the network, such as the iPhone, the router could be forced to stop "beam forming" because you have too many units connected or similar. That could give you worse performance on the existing units, even though the iPhone is not transmitting/receiving any actual data.