1. In Azure Portal, locate and select database db3.
2. Select Security and Advance Data Security, and Click Enable advanced Data Security Protection

3. Click the Data Discovery & Classification card.
4. Click on Add classification in the top menu of the window.

5. In the context window that opens, select the schema > table > column that you want to classify, and the information type and sensitivity label. Then click on the blue Add classification button at the bottom of the context window.
Select/enter the following
Schema: SalesLT
Table: Customer
Column: Phone Information
Information type: Contact Info

6. To complete your classification and persistently label (tag) the database columns with the new classification metadata, click on Save in the top menu of the window.

References:
https://docs.microsoft.com/en-us/azure/sql-database/sql-database-data-discovery-and-classification