All use values from field value lists are sorted in ascending order on either field 1 or field 2. No other options are possible.
Two possible ways to deal with this limitation:
Put a field on top of the pop up menu or drop down list that displays the desired data in the desired format. (I'd use a date field with an actual date and use data formatting to show it as MonthName Year.) If you use behavior settings to deny Browse mode access to this field, clicking on it will cause the drop down list hidden behind it to pop to the front and deploy. When you select a value, it disappears back behind the field and the corresponding data displays in the field on top of it.
Don't use a value list for selecting this value. Portals in a popover can work much like a drop down list or pop up menu and you can set up the fields that make up the portal row into a button, that when clicked sets your field to the desired value. Since you are using a portal to display your data, you can sort the rows of your portal in any order that you want.
For more on using alternative methods for selecting values from a list, see "Adventures in FileMaking #2 - Enhanced Value Lists".