My 950XL has just started having a similar problem where I put it on speaker and I can hear the caller, but they can't hear me. Then I turn off speaker and they can hear me again. If I try speaker (on same call) then it sometimes works where we can hear each other. When I turn speaker off again, then they can't hear me and I have to put speaker back on. If I hang up and dial again, then all is good until I try to use speaker again. Not sure if that made sense, but I've just started having problems with speaker phone function as well.