<!-- If ComboBox wasn't broken: -->
    <mx:ComboBox id="phaseCombo"
        dataProvider="{chain(['---'], phaseList)}" />

<!-- Because ComboBox is broken: -->
    <mx:ComboBox id="phaseCombo"
        dataProvider="{chain(['---'], phaseList)}">
        <mx:creationComplete><![CDATA[
            chainListener(event.target, "dataProvider",
                          CollectionEvent.COLLECTION_CHANGE,
                          ignoreArgs(event.target.invalidateSize);
        ]]></mx:creationComplete>