In an electronic device and a method for operation of the electronic device according to various embodiments, the electronic device may comprise: a sensor module for sensing whether an external object approaches the electronic device; a communication module for cellular communication; a first antenna for the cellular communication; a short-range wireless communication module for short-range wireless communication; a second antenna for the short-range wireless communication; and a processor, wherein the processor is configured to: check by means of the sensor module whether the external object approaches so as to be within a specified range, while transmitting a cellular signal with specified power through the first antenna; output a specified signal through the second antenna at least on the basis of determining that the external object has approached so as to be within the specified range; acquire, by means of the second antenna, a signal returning after the specified signal is reflected by the external object; transmit a cellular signal having been adjusted to have lower power than the specified power, when the phase difference between the specified signal and the reflected signal falls within a specified range; and refrain from adjusting the specified power, when the phase difference falls outside the specified range. Various other embodiments are also possible.