I would use the Network Assessment tool to test your network and the Microsoft Teams website has the ports and IP's to whitelist. These are for the Teams client as a whole. All of your mobile/ landline voice traffic for the direct routing is sent through Teams at the moment.
You do also have the option to use Media-bypass to have the voice traffic be point-to-point, but there are more network technicalities to consider.
Network Assessment Tool:
Firewall Ports & IP's: