Decode Null value

Summary

Decode if phone number field is null or not

Content

Hello - I'm having trouble figuring out to output a value if a persons phone number is null or not.  I'm writing an interface to a vendor and if I provide a phone type but no phone number, the import writes out an error message.  In order to avoid these messages, I need to determine if the phone field is null.  I've tried many functions without any luck.  Does anyone have a projection or input as to how I can output a static value if a field is null or not?  Below is what i was thinking, but is never