Callers can't hear me on Bluetooth

I have an iPhone 6. In my car (2016 Nissan Rogue), I can play my music and hear my callers just fine over Bluetooth, but they cannot hear me, so I have to put the phone on speaker to have a conversation. I have tried disconnecting and reconnecting my Bluetooth connection on both the device and in my car and restarting my phone, but it still doesn't work. My car just had a repair and when I tried it today, it worked for about 5 mins before it went out again. Does this sound like a phone or a car issue? Thank you!