Most reliable option is to look at where the power comes in yourself. 4 cables in (all of which should pass through the meter), means there is 3 phase coming in. If there's only 2 cables, then it's only single phase.

If there's not a low voltage 3 phase transformer near by, then expect a 5 digit cost. My neighbour just got quoted 18'000 to get a transformer installed to get 3 phase next to an 11kV line.