More often power off your phone or set it to airplane mode with Wi-Fi OFF and Bluetooth OFF. Even in standby mode, your phone emits RF energy because it is constantly searching for service or new messages. If you do not need your cell phone, simply power it off. This also applies to all other wireless devices whereby the Wi-Fi antennas can be powered off. Wi-Fi enabled laptops, tablets and other wireless devices (such as gaming devices) are always transmitting even if you are not using them, so remember to power them off.
The energy of electromagnetic radiation is determined by its frequency; ionizing radiation is high frequency, and therefore high energy, whereas non-ionizing radiation is low frequency, and therefore low energy. The NCI fact sheet Electromagnetic Fields and Cancer lists sources of radiofrequency radiation. More information about ionizing radiation can be found on the Radiation page.