Android 6 - phone audio output ONLY when on speakerphone, otherwise no audio heard

Question

Problem is with a current Android 6 Lenovo.

With speakerphone button OFF:

• No audio on dialing
• No ringing
• No hearing other person talking
• Remote person can hear me (mike working)
  

With speakerphone button ON:

• all works fine.
  

Default install. Have PC with Win 10 in same room - works fine (no issue with dialing, connecting, blocked ports, etc. Have Android 4.4 phone - works fine.

Possibly related:

http://www.zoiper.com/en/support/answer/for/android/11/SIP_-_No_audio_or_one_way_audio

(nothing seems to work)

Config->Audio->Audio Driver
to “External Java Driver” -- no improvement

http://community.zoiper.com/2671/zoiper-not-ringing-android?show=2671#q2671

http://community.zoiper.com/1434/android-zoiper-fails-to-re-connect-after-network-loss?show=1434#q1434

http://community.zoiper.com/2639/output-audio-microphone-working-android-vernee-speaker-fine?show=2639#q2639

Above 1+ed seems related.