In order for a handlebar mounted cycling computer to operate as a phone, I would need to use either BT or wired headphones, or I'd have to remove the device from its mount, clear the tether and hold up to my ear. I'm sure as hell not wearing headphones and its far easier to use a top tube bag to hold my phone, taking it out if I get a call. There's zero point to combining the two devices as far as I'm concerned.