Summary: No (sorry!).
At the moment, it isn’t possible to bulk-import sentences or phrases into the app, either via CSV or through an API (or any other method).
All content needs to be added directly in the app, with cards created individually, one by one.
This allows you to attach images, audio, and other details as you go.
This is actually a core part of the Fluent Forever method.
The act of creating each card yourself, choosing or searching for images, and thinking carefully about how to visually represent a word or sentence plays an important role in forming strong, long-term memories.
It may feel slower at first, but it is deliberately designed to make the learning stick.