Use set the Min Password length policy to min of 12 characters to encourage the use of a phrase.
This is currently a product limitation, however an Enhancement Request had been created for this to be considered in a future release of the product ER ID: 269656
Our product management team reviews open enhancement requests and considers them for inclusion in a future product release. There is no guarantee that a specific enhancement request will be implemented in a future release. For more information regarding our enhancement request policy, refer to our Global Support Guide on the Support Portal at https://support.oneidentity.com/.