One of the meanings of the phrasal verb to listen in is "to listen to the radio".
Once the preposition to is already present in the definition, is it needed after the phrasal verb as well?
Q: What do you think she is doing now?
A: Listening in (to?) a drama show as usual.
I've never used this phrasal verb before, but something makes me doubtful whether the preposition to is obligatory here; although most certainly I am mistaken.
Could you elucidate that for me, please?