How to Sort a Picklist

I have a lookup field in a form, which pulls values from a Text field in the child form. When this field shows a dropdown selection during Add, the picklist default sort is by record "ID", not the Text field. I can't find a way to Sort this picklist. I've tried adding a Clear statement and rebuilding with the Field.add() function, but this retains the original sort (by ID).

Do you know if/how I can sort a picklist?