Bill,

Is Primary_Cell__c a boolean field, and do you mean in a UI-field formula field? If so what you have should work. Another good option if it works for your use case is to use conditional merge syntax. It’s in the format of {{#field_name}}show_when_true/has_value{{/field_name}} {{^field_name}}show_when_false/empty{{/field_name}} and you can use it wherever you can use merge syntax. Look under Sections of this tutorial to see an example.

Thanks!
Amy