[dTal]

> My Moto phone always blanks the screen when you are talking,

I don't know exactly what model of phone you have, but most smartphones have a proximity sensor which is used to intelligently blank the screen only when it is at your head. Not uncommonly this sensor gets dusty or dirty, causing the issue you describe.

[Suppafly]

It maybe something to do with that, because it doesn't happen if I use the phone sitting on the desk, but once I've tipped it to my ear, even after I tip it down to look at the screen it'll lock the screen, I unlock it, it immediately locks it again, I unlock it, etc over and over.