Why does she used "Was it~" instead of "Did you learn"?
Native speaker’s answer
Rebecca
She says "was it" here at the beginning of the sentence because she is asking the sentence "did you learn..." in a different way, and "that you learned" is implied at the end of her sentence here. So the full sentence here should be "was it just phrases that you learned?" This sounds a little bit more casual than "did you learn".