It happens from time to time. I'm talking to someone and their cell phone rings. After they glance at the screen to see who's calling, I get the inevitable, "Sorry, I have to take this," and the person who was talking to me is now talking to someone else.
Now, there's not necessarily anything wrong with my former conversation partner talking to whoever is calling — it could be their spouse, parent, boss, someone they've been trying to get in touch with, etc. Regardless, the point is that the person was focused on talking to me and has now chosen to turn their focus elsewhere.
Considering how automatic the above actions are for most anybody today, how would I feel if you and I were talking, and you refused to look at your phone when it rang or even went as far as turning it off so it wouldn't be a distraction? I would feel quite honored and respected that you would be willing to focus on me for that period of time.