This can be accomplished through the use of a single select field and on screen business rules.
First you will need to create a single select field that has choices which are labels for the text you wish to insert.
Like opening greeting, close issue, request for more information etc...
Next you will want to add that to the form and save it.
Finally you will need to build the business rule to drive the action.
1. The rule will be "On Screen" type, using the on screen trigger, "On Create" and "On Update".
2. The criteria will be the name of your single select field having a particular choice.
3. With the action of set field value/field to insert text in to/ the text you wish to insert. You can have multiple actions to update multiple fields.
You will need one rule for each of the Quick Description field choices.
Attached to this article there is a video walking you through the process to add this to your work spaces.