Since Windows 7 (I believe), the default Windows config doesn't allow apps to mark their own DSCP. You have to create a QoS policy for the application or destination IPs. There are a ton of resources on the web if you search for "Windows set app DSCP" or similar, but I can't seem to find the official Microsoft one at the moment, other than the one specifically for Windows Server found here: https://docs.microsoft.com/en-us/windows-server/networking/technologies/qos/qos-policy-manage
As for the MPP phones, you can set them in Control Hub, but, depending on your VLAN configuration, you might also have a dedicated Voice VLAN which sets the DSCP based on the port/VLAN combination. The MPP supports LLDP to determine the Voice VLAN advertised by the network, which is an easier way to accomplish it in very large deployments.
Edit: Here is an old support port that describes the process for Jabber. You would just have to alter the EXE for the Webex app. https://community.cisco.com/t5/collaboration-voice-and-video/enable-dscp-marking-in-windows-os-7-8-10/ta-p/3164942