Hi Jordan,
I'm pretty sure this is because in your microflow you are not creating an Object based on the Entity System.FileDocument (or entity that has a Generalization of FileDocument). To be able to see some results in the File field you need to supply a FileDocument Entity:
However, to be able to upload a file, you would need to implement a page with a File Manager component. (in the Save button you could use the microflow above, so that you can pass the file uploaded to the Data Import activity):
I hope this can help you use this great tool for importing your Data, if you have any questions feel free to ask. Best regards!