Comment 1 for bug 1720684

Bluetooth audio and profile selection is actually the job of pulseaudio, not bluez (surprisingly).

Also, A2DP has always been preferred over HSP/HFP but the availability and detection of A2DP has been historically buggy. So the selection might not turn out as you hope. AFAIK fixes for this already exist in 17.10 and in 16.04:

https://launchpad.net/ubuntu/+source/pulseaudio

Unfortunately it seems 17.04 has been neglected in this area. Although to be fair 17.04 is also end-of-life soon:

https://wiki.ubuntu.com/Releases

Please try live-booting the latest 17.10 image and tell us if that has indeed resolved the problem for your hardware:

http://cdimages.ubuntu.com/daily-live/current/