Why does Sunmi not have Yubin's cell phone number?

Wonder Girl's Sunmi revealed why she doesn't have fellow member Yubin's cell phone number. 

During a live airing of 'Lee Guk Joo's Young Street' on July 11, a listener asked, "How did you save your members' names in your contacts?" Sunmi responded unexpectedly with, "I don't even know Yubin unnie's cell phone number." 

She then explained, "Yubin unnie got a new phone not too long ago, and since we are currently promoting, there's no need to know her number because I see her everyday." 

Makes sense..?