Just noticed on tech community you can now add DSCP tags to SfB Online IP Phones and here’s a quick walkthrough. Tech Community article https://techcommunity.microsoft.com/t5/Skype-for-Business-Blog/Configuring-Voice-Quality-of-Service-for-Skype-for-Business/ba-p/118000
Setting the DSCP marking for IP Phones will help with Quality of Service tagging but for QoS you also need to ensure network is configured end to end to honour the IP markings.
1. Connect to tenant via PowerShell –
More details on how to connect to remote PowerShell into SfB Online https://technet.microsoft.com/en-us/library/dn362795(v=ocs.15).aspx
2. Check existing settings using Get-CsUCPhoneConfiguration
By defaults VoiceDiffServTag is set to 40
3. run the following to change the value
Set-CsUCPhoneConfiguration –VoiceDiffServTag 46
Then i ran Get-CsUCPhoneConfiguration to check the configuration change.
You can set the DSCP marking to what you require but the default usually set for audio at 46.
Two other greats posts on QoS in SfB Online