I just bought this phone here in the USA and am having this issue. It does not seem to be an isolated problem. No mic function while on speaker phone and cortana learning my voice was a terrible experience. I have had many windows phones, this being the 4th from Nokia, and this is the biggest problem I have encountered.
What can we do to get this resolved in a timely manner and not be without a phone in the mean time? Being loyal customers and all.