[Lewisham]

From my POV, I felt that the phone interviewers for my internship were chosen arbitrarily (mine were from New York, when I was trying to get a spot in the Mountain view campus).

The reasoning appears to be that you're either good enough or you're not, and that it doesn't matter who interviews you for that to be true. However, the difficulty was really variable: interviewer 1 asked lots and lots of algorithms questions which I wasn't doing well on, caused him to become obviously annoyed with me. 2 seemed fairly ambivalent throughout. 3 really worked with me to try and get answers out of me (even though I was incredibly nervous).

I don't see why phone screens are not with prospective teams; they're the ones that will have to deal with you and have the best idea of what skills they need. Maybe they're trying to avoid people building up little fiefdoms? I generally came out feeling the way you do (and the way the OP does). It seems random, and for a company that (rightly) prides itself on the quality of its data and making data-led decisions, it makes it sting doubly.