As installed, default instances of SQL Server ('MSSQLSERVER') use TCP port 1433 but named instances will use dynamic ports. These can be reconfigured using Configuration Manager.

Commonly on Active-Active clusters I'll use static ports from 1450 and upwards, assigning a port to each instance. You can use any range you choose though, and indeed I think you can use the same port for each instance as long as the IP address is different, it's just a preference of mine to use sequential ports for each instance.