You would not be able to learn Japanese through simple repetition of phrases alone. However, learning few set phrases would be a good start, but any serious Japanese student would be required to focus on grammar as well.
The Japanese language school would help you understand that grammar and sentence structure has been relatively different from English. It makes the language more complex for English speakers. However, it would still be fun to learn. You should concentrate on the basic Japanese grammar early and start building on your grammar skills gradually. Grammar has been the only way to make phrases, sentences, and complete conversations with practice.