BGC IT,
It is not clear what is wrong in the big picture here; there is simply not enough information. The problem could occur on many levels that are not obvious. In the SSID profile for WLAN under advanced, please enable "Advertise QBSS Load IE" and do the capture again so TAC can see the load on the WLAN in the management frames on the access point:
http://www.arubanetworks.com/techdocs/ArubaOS_64_Web_Help/Web_Help_Index.htm#ArubaFrameStyles/VirtualAPs/SSID_Profiles.htm?Highlight=Advertise QBSS Load IE
Also, try to do a packet capture with an external device of the entire channel (air monitor or laptop with packet capture software); NOT the access point that is servicing the client, so that we can ensure that all traffic is captured.
The packet capture is only part of the picture. It is best that you open up a case with support in parallel so that they can gather all of the information and understand what factor(s) could be leading to your issue. If there is intererence for example, we could not tell by just a packet capture. Unless we have the logs.tar and the tech-support from the access point when this call takes place, we do not have a logical starting point. This could be a phone software/configuration issue, an interference issue, an Aruba controller configuration issue, or a wired traffic issue, etc. VOIP is the most difficult type of traffic to troubleshoot and it is painful to pass pieces of data back and forth without having all the info at hand to understand what is going wrong.