Let me try to break this down.
MorrieStranded - Incoming call from PSTN to Phone. The PCAP shows an audio stream from 172.16.1.16 (PBX) to 172.16.100.226 (Phone) and vice versa. In both instances each stream is showing wrong sequence and timestamps for RTP packets.
DriftingCrawley → Incoming call from PSTN to Phone. The PCAP shows an audio stream from 172.16.1.16 (PBX) to 172.16.100.222 (Phone) and vice versa. In both instances the streams show to be OK.
AcquireShaving - Outgoing call from PSTN to Phone. The PCAP shows an audio stream from 172.16.100.222 (Phone) to 172.16.1.16 (PBX) to and vice versa. In both instances the streams show to be OK.
In regards to the two PCAPs for .222, it looks like standard NAT/firewall issues. Outgoing request has no issues because it initiated the request, opening up ports, etc. Incoming request has issues because ports aren’t open, something closed or it’s not routing incoming requests properly.
The issue with .226 is out of sequence packets and wrong timestamps. Real time doesn’t play nice with that.
Bottom line is you got some networking problems you need to figure out.