Losing Internet connectivity - wifi

I just added a third wireless printer to our network and all of a sudden I'm having dropped Internet connections on two of our laptops. They still connect to the network, but Network Magic verifies that there's "No Internet Connection." - I'm using a Linksys E2000 router and a Netgear WN3000 extender. All of the affected devices are using the extender. The problem will correct itself if I unplug the extender and plug it back in, so I replaced the extender with a backup Netgear extender, but get the same problems.

The only thing that I've been able to isolate is the possibility that some of our cellphones might be interfering with the wifi signal? The two laptops that are dropping Internet have iPhones near them (4G?) Could this be a problem? I'm just at a loss - tried talking to Linksys about the problem but they want $$$ to talk, cheaper to just replace the main router if that's the problem. Every so often I see a message saying that another device has been assigned the same IP as one of the laptops affected. I bumped the 'number of IPs' on the main router up to 100, which should be plenty.

This is a T1 connection. Any ideas?

 

Possibly try setting some devices to static IP addresses outside the DHCP range for the IP conflict.
Checked firmware on the routers/extenders and drivers on the adapters for latest versions?
Change channels on wireless?

 

Yes, the firmware is up-to-date. This is very strange, but the problem began when we had a new associate join the firm, and she has an iPhone that she keeps next to her laptop. The only other iPhone in the building is one that my wife keeps next to her laptop, and these are the two laptops that are having problems. We moved the iPhones, and the problem seems to have disappeared. Crazy, huh?