1. Because Douyin's algorithm and user data analysis capabilities are strong, it can quickly match the corresponding user information and product recommendations based on the mobile phone number entered by the user.

2. As a social entertainment platform, Douyin needs to obtain the user's mobile phone number for user identity authentication and account binding to ensure the security of user information and normal use of the account.

3. In addition, Douyin also uses the user's mobile phone number for precise advertising and personalized recommendations, and displays relevant products and services to users based on their interests and behavioral habits to enhance user experience and advertising effectiveness. In today's digital age, many Internet platforms require users to provide their mobile phone numbers, which is not only to ensure the security of the user's account, but also to provide more personalized services and recommendations. Users can choose whether to provide their mobile phone numbers to Douyin or other platforms based on their needs and privacy awareness.