May be wrong, but the User Guide for the phone doesn't mention the it has IR capability so that should be one less worry for you. Also radiation from the WiFi and phone signal wouldn't be any stronger to cause concern just because the cover is off. You have it right next to your face when you use it normally
Chances are that you could harm the phone more than it could harm you, especially if you poked around, even just using your fingers let alone tools.
You have to consider that the systemboard has power on it at all times even if the phone is switched off, as the battery is permanently connected to the board and doesn't go through an isolating On/Off switch. The Power switch just tells it to turn on, it doesn't actually supply the power.
If you wish to work on the phone or even touch the systemboard disconnect the battery first, unless you need power for testing purposes. Even then be aware of ESD when handling sensitive electronics. Wear a wrist strap connected to earth to minimize the chances of ESD destroying a component.
Hopefully the phone is still OK because you should be.