OK. First, I think phrasing is too advanced for someone who is "quite new to ballroom dancing". This is something you shouldn't really worry about until after you've got down some steps, technique, etc. and don't need to think so much about basic stuff like that. Then you can worry about dancing on phrase to the music. And what constitutes the "smallest segment of our 4/4 music" depends on how you want to break things down and define things. By the time signature's definition, the smallest "unit" is the quarter note. Measures are certainly smaller units than phrases and phrases don't have to be two bars, they can be 4 our 8 or 12 or 16. In speech or writing is the smallest unit a sentence, a single word, or one of the syllables that make a word? For music that's like is it a phrase, a bar, or a note within the bar? For our case here, recognizing what dance goes with what music, I think the phrasing is almost irrelevant. You don't need to hear the phrases to pick out the beats, tempo, and rhythms that identify a song as a particular dance. As long as you can pick out the first beat of each measure so that you'll be dancing on time, the musical phrasing really isn't important for a beginner. Gan, this is useful stuff to know eventually, but I wouldn't worry about it right now if I were you.