50_50,
This (sort of) happened to me a couple of times. I'm in a different field and still in the app process, but what I can tell you so far is that for all of my phone convos, I spoke with the professor about their lab and research interests. They didn't mention any other profs or ask about my interests that would be un-related to theirs. I don't think they'll wonder why you didn't list them in their SOP - if you didn't list anyone than obviously you were addressing the program as a whole and trying to be broad. Be honest about your interests, let them guide the conversation, and to prepare read his/her work and know what you like about the program as a whole. He/she will probably be happy to know that s/he was right in guessing your specific interests. Prepare questions about the lab and feel free to ask about how collaborative the program is (like if students work with multiple advisers) but I wouldn't ask specifically about another prof unless they bring it up. Good luck!!