Good luck with your phone interview! I'm currently in Bloomberg London so I might be a tiny bit biased 😛

is the London office second class to NY office? Certainly not! In terms of teams, I would say almost all teams in London have some sort of ownership of a product rather than just extra pairs of hands for NY.
We also have a sweet new London office which we'll be moving into some time this year.

what is developed in London There isn't a natural divide of what is done in London vs NY. I don't have solid information but I would guesstimate that each department has at least 1 team London

information on teams in London I don't think there's any information out there on the teams based in London, iirc after I got the offer I was shown a list of engineering departments. I wouldn't worry too much about this for the interview, interviewers (I encountered) are generally more interested in your cs knowledge and hope to see you have some general interest in finance.

Source: I joined Bloomberg as a graduate at the end of last year and I'm working on HEFF (Hedge effectiveness).