There are no regulatory requirements for how your financial services organization should handle oral complaints from a UDAAP perspective. However, a best practice may involve tracking oral complaints, including those that may be phrased as more innocuous questions, using the same system that you use for written complaints.
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These best practices are described in detail in BAI's comprehensive courseware catalog, course 20383 - UDAAP: How to Prepare Your UDAAP Program.