I've got the exact same problem with my Z2. The other party cannot hear me when I hold the phone to my ear -- if I turn the call on speaker, everything works fine!
Also, the other party hears a very strong echo of their own voice, but only when the call is not on speaker.
It is absolutely beyond me, how something this simple has gone through the quality checks at Sony. Seriously, a 600€ phone that you can't use to make normal phone calls. Are you serious?
And yes, I also tried turning off noise cancellation in the call settings, did not help really much...
The fact that it DOES work when using the speaker tells me that it is "just" some software bug that should be fixable (and not a defect microphone).