Simple Function for Field equals another Field within the same Module

Simple Function for Field equals another Field within the same Module

Our website uses Gravity Forms. The Gravity Forms -> Zoho CRM integration does not support Pick Lists. So, I have a dropdown menu on my web form which contains the same selections as the corresponding Pick List in Zoho. Upon form submission, a new Lead is created and the Gravity Forms Integration maps that dropdown selection into a custom Single-Line field (Field A)

I want to create a workflow which, upon Lead record creation, checks the condition that Field A is not empty. If Field A is not empty, I want the Instant Action to be a function that simply executes "Field B = Field A"  where Field B is the Pick List with matching values.

It was suggested that I create an individual workflow with a 'Field Update' action for each selection in the Pick List (example: If Field A = "List Item 1"; Field Update Action: Field B = "List Item 1").

However, there are 21 items. I'm not sure creating 21 individual workflow rules/Field Updates is the right way to go about this. It seems like I should be able to create a single Function-based workflow. 

Is this possible? Any suggestions and help is much appreciated. Thank you in advance!