As I understand it the Elemnt/Bolt will use the data from a connected speed sensor instead of the GPS speed. I don't think having a smartphone paired matters at all as to when the device decides it'll use the speed sensor, did you read that somewhere ?, it really should have nothing to do with how the device functions to determine speed.

As well, I've read from other posts, that the speed sensor is actually slower at kicking the unit into auto-pause as compared to using GPS alone.