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[LordZsar1]

I did not make that one up, I am not the one to ask. The word was established as soon as 1980, earlier mayhap, and is therefore at least eight years older than I am.

"Phantasie", recently "Fantasie", means "imagination", the corresponding images ("figments") are usually referred to as "Phantastereien" (more often: "Einbildungen", "Hirngespinste", but those are obviously not related to the radical in question).
It is not associated with genre classification in any way I know about - it might be interesting that in literature, fictional situations are categorised as "imaginär", whereas "phantastisch" refers to those that are impossible to occur at the given time frame or with a time frame in the future.
As that is, there is indeed no german equivalent for the term "Science Fiction" and at least in eastern germany before 1990 it fell under "Phantastik" as well - though that appears to be not the case anymore.