try once:-
USE master
DECLARE @portNumber NVARCHAR(10)
EXEC xp_instance_regread
@rootkey = 'HKEY_LOCAL_MACHINE',
@key =
'Software\Microsoft\Microsoft SQL Server\MSSQLServer\SuperSocketNetLib\Tcp\IpAll',
@value_name = 'TcpDynamicPorts',
@value = @portNumber OUTPUT
SELECT [Port Number] = @portNumber
GO