Single. 3 phase is uncommon outside of industrial settings.
Residental houses in the US are wired with a 240V center tapped
transformer. This gives a single phase output, with the center tap
as the neutral to give 120V.
The average house fly lives to be about 1-2 months old. That
includes the average of swatted flys.It shouldn't stay for long and
another idea that may help would be letting it out of the house if
it stays for too long.