Which type of natural language processing (NLP) entity is used to identify a phone number?

In Natural Language Processing (NLP), entities are pieces of information extracted from text, such as names, locations, or phone numbers. According to the Microsoft Learn module “Explore natural language processing in Azure,” Azure’s Language Understanding (LUIS) supports several entity types:

Machine-learned entities – Automatically learned based on context in training data.

List entities – Used for predefined, limited sets of values (e.g., colors or product names).

Pattern.any entities – Capture flexible, unstructured phrases in user input.

Regular expression entities – Use regex patterns to match specific data formats such as phone numbers, postal codes, or dates.

A regular expression is ideal for recognizing phone numbers because phone numbers follow specific numeric or symbol-based patterns (e.g., (555)-123-4567 or +1 212 555 0199). By defining a regex pattern, the AI model can accurately extract phone numbers regardless of text context.