Try portName (.1.3.6.1.4.1.9.5.1.4.1.1.4)
You will need to specify the correct index. Here is a sample snmpwalk:
> snmpwalk -c public 14.32.6.12 portName
CISCO-STACK-MIB::portName.1.1 = STRING: Test
CISCO-STACK-MIB::portName.1.2 = STRING:
CISCO-STACK-MIB::portName.3.1 = STRING: Net Analysis #2