How to display a note if a row does not exist? SQL Server -

i want display phone numbers of customer(customertable).

but if there no phone number because customer hasn't left one, want display note saying "no phone number".

i've tried command

select phonenumber  customers if phonenumber null raiseerror 'no phonenumber'  -error

but error:

"phonenumber" not valid columnname

and guess raiseerror not proper way display note (?!)

please help

sorry poor english.

why not use coalesce return first non-null value?

select     coalesce(phonenumber, 'no phone number') customers

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