OK, from the figures shown in your call status, the jitter buffer underrun is surely caused by silence suppression. the ratio of packets received and sent is roughly about 50%, which means the callee suppresses silence 50% of time.
You have very little packet loss (only 1 packet), but did experience some network jitter (480+ ms), which caused some packet dropped (6%). This could degrade your voice quality by some level.
Usually, silence suppression should not degrade voice quality, unless there is a high level of background noise on the callee side. You might initiate another call but with callee at a relatively quite place, just to confirm silence suppression does not affect your call.
Also, you can try to call a different destination (local or international), and check on quality... after all, VoIP cannot eliminate network impairments, but mitigate it at its best ...