I'll try with the expressions :)
- " Are you on the phone?"
I think it means "Do you have a phone nearby, can I call to you"?
- "What difference does it make?"
It will be better to explain this in the contects you met it.
In other way I could say "If I use A instead of B, how the result will change?"
May be I'm not right :), I'm not a native speaker.
- For Teachers