Filters for text-driven fields are not automatically generated. Generally isn't a reason to filter on free text. Free-text fields can store unlimited variations of a single response. Typically exports are all you'll need for a free-text field. However, there may be occasions where you wish to query on very specific text. This can be accomplished using Subquery Filters in a configurable joins query.
Example - Organization Name is ...
One approach is to use a "Formula" Aggregate filter:
Example - Last Name Contains...
You can use the LIKE operator, with or without a wildcard (%), to find text that contains a specific value. For instance, here's an example for looking for records whose last name contains "Sam":
Example - Last Name Starts with..."
Another looking for last names starting with "Sam":
Last Name Starts with Letters A-F
Another looking for last names that start with the letters "A" through "F":
Example - Organization Name is...
In this example, a literal export was added to check against a specific school name ("An Example School").