Stein,
For fine control of my network, and for QoS to work at its best, I assign a RTP (UDP) port range to my phones. For example. My phone uses RTP ports 10000-10019, My wife’s uses range 10020-10039, and so on.
If your phones have the ability to assign a RTP (UDP) port range, I suggest you assign it manually, then go to the PEP and assign those UDP ports, by creating a custom rule and in my case for example, I would prioritize to “High” UDP port range 10000-10039. The reason for this is because youtube and other video apps use a whole range of UDP ports, but I don’t want video traffic messing up my voip calls. This is what I mean by fine tuning QoS and it works very very well. Let me know if that makes sense. I am attaching a picture of my QoS settings for these ports.
Regards!