With a wireless mic, the microphone takes in a signal on the transmitter. Depending on the transmitter, it may accept line level, mic level or both.
The transmitter then either translates that in to radio waves or digitizes it and transmits the digital audio. The exact means is defined by the particular microphone system and is basically irrelevant to your purposes. The important part is that the receiver knows how to read that signal and translate it back in to an analog audio signal that is produced by the receiver.
Similar to the transmitter, the level of signal that the receiver produces is dependent on the receiver and doesn't necessarily match with what went in to the transmitter. You should not need to (nor should you) send any phantom power (+##V) to the receiver as the receiver uses its own power. It is most likely giving a line level output, but that isn't a guarantee.
If your transmitter supports both line and mic level, you should choose whatever level your input actually produces to ensure the least noise. This selection determines how the signal is translated to radio waves and generally, this processing and transmission is the easiest time for it to pick up noise. Using incorrect settings will result in a too loud signal that clips or a too soft signal that gets excess noise.