Currently Being ModeratedMay 2, 2013 2:41 PM (in response to Klaatu1947)
I found a good resource to help troubleshoot the wifi issue you are experiencing with the iPhone 5 named
iOS: Troubleshooting Wi-Fi networks and connections found here: http://support.apple.com/kb/ts1398
I would recommend the Basic troubleshooting section first, and then the section farther below labeled After joining a Wi-Fi network, you notice the signal strength is weak or fluctuates.
Within that section is another link to an article to check for potential sources of interference on that 5GHz spectrum named AirPort and Bluetooth: Potential sources of interference found here: http://support.apple.com/kb/HT1365