You can create a new field in the pivot table as an alternate method, but you may have to open the full menu to see the group and outline option
In the pivot table toolbar there is a drop down menu where you can create calculated field
in the feild you can use this formula (assumes the date field is named "Date", you will have to change it)
=IF(month(date)<4, "QTR1",IF(Month(Date)<7, "QTR2",IF(Month(Date)<11,"QTR3","QTR4")))
And hit okay. A new field will be added to your pivot table showing quarters as per the formula.
See the pivot table help topics, they are quite useful