Power Automate - Condition, check field in body

[Reynir15]

Hello, I have a Flow that is fired on the Phone Call Create.  I want to check if the phonenumber field has a value or not in the Flow.  The problem is that you can not check if the phonenumber has a value (is null) because it is not included in the body if it is empty.  What is the best way to check if a field exists in the Phone Call body in a condition ?

Thanks, 

Rey