Answer:
The ratio of a transformer is simply the number of turn in the primary divided by the number of turns in the secondary, i.e. the turns ratio. For instance, if the turns ratio from primary to secondary were 10:1, and the transformer was supplied by 120VAC, 1A, you would expect an output of 12VAC, 10A. Of course, there are other factors to consider, but this is the basic premise.
Note: There is no such thing as a multi phase transformer, so including the phrase "single phase" in the question is moot. So called "three phase transformers" are actually three independent transformers operating in tandem. They have separate windings, separate cores, and separate magnetic fields. They might be enclosed in one box, but they are still independent of each other.