How to troubleshoot inbound only dropped voip calls?

[OrthoC]

Hello,

So I am very new to FortiOS and FortiNet products as a whole. So bare with me if I ask some questions that I "should" know.

I am trying to troubleshoot the only problem I am having with a newly setup FortiWifi 30E firewall acting as a small gateway/firewall for a satelite office of 10 people.

The firewall is running in Proxy Inspection mode with Central SNAT'ing enabled. Literally all of my other services are working perfectly, however I have a problem where only random inbound VOIP calls are being dropped after 4-10 minute period (Telus Business Connect). No other symptoms are appearing before the dropped call either (no loss of quality, jitter, etc). I've had the internet connection tested and its working well within its range (line is capable of 100/50, but I'm only running 25/10). 

I'm trying to grab a debug log via flow capture (through Putty's SSH Logging) however it seems I have to specify the amount of packets to capture, which doesn't guarantee me to capture what I need (I'd really like to turn on some kind of logging that captures everything related to a few VOIP phone's IP's traffic, but I cannot seem to find a method to capture everything).

If anybody can suggest how I can capture more detail without having to keep re-activating the capture after X packets.

Thank you