Bose says there are two dedicated microphones for picking up your voice, which work with two of the noise-cancelling microphones "to dramatically improve voice pickup."
In Bose's words, "a beamform-array isolates your speech, suppressing everything else that's audible. A rejection-array adds a second line of defense, tracking then blocking the most disruptive remaining sound — from a coffee grinder to other dialogue nearby. It all happens in real-time — adapting as you move, turn your head, and your environment changes."
Essentially, Bose is saying that phone calls with the 700 headphones will be a lot clearer for you and for the person you're speaking with, especially if you're in a noisy place.