In the early days of Bunq, people in my contact list were flagged as bunqers, when the app recognised their phone number. So I could easily see which contacts are fellow bunqers. Even if they had never given me their IBAN, I could easily send them payments or requests, straight to their app.
I think this feature was killed because it violated with privacy regulations. Which actually is a pity, it made things easier for Bunqers who didn't know from each other they were Bunqers. If privacy was the only reason to kill this: I would be happy to opt-in on this feature, should it return.