https://ankidroid.org/docs/manual.html#importing
It needs to be an *.apkg file.
AnkiDroid doesn’t support the Anki 1 file format *.anki.
Your options are:
1) install Anki on a computer, install the deck, create an AnkiWeb account, sync to web, AND THEN sync to AnkiDroid.
2) Find the same deck already converted to Anki 2 format.
Option 1 is the best way, so you can be doing your Anki reps anywhere and if you lose your phone you’ve still got your decks.
For Option 2, I’d search the forums to see if someone has already done this for you. I’m new to TextFugu, but I’d be surprised if that resource wasn’t already available.