My guess would be "Miluji tě" for "I love you". In English we put a lot of emphasis on "those three words", but I believe that normally in Czech you would exclude the "já" in everyday speech, so it would be those two words.
Tamta is accepted in the reverse direction as well. This course is pretty consistent in regarding both ta and tamta and some more as both "the" and "those". I found "tamta" less natural in this sentence.