Decoupling Real Identity: Your phone number is arguably the strongest link to your real-world identity. By keeping it private, you maintain a layer of pseudonymity on Telegram, allowing you to interact with others without immediately revealing who you are outside the app. This is vital for journalists, activists, or anyone who values privacy in their online interactions.
Personal vs. Public Sphere: It allows you to separate your personal life (where close contacts might know your number) from your public interactions (e.g., in large groups, channels, or with casual acquaintances found via usernames).
Protection Against Unwanted Contact and Harassment:
Spam Calls/SMS: If your phone number is exposed, it can be harvested by spammers, telemarketers, or scammers, leading to an influx of unsolicited calls and text messages.
For individuals who might be targets of harassment or doxing (maliciously publishing private information), phone number exposure can be a direct pathway to real-world threats, stalking, or unwanted contact.
Targeted Attacks: Malicious actors can use your exposed phone number to research other online accounts linked to it, potentially leading to social engineering attempts or credential stuffing attacks.
Security Against SIM Swaps:
The Phone Number as an Account Key: Many online telegram number database services (including Telegram for initial login) use your phone number for authentication and account recovery.
SIM Swap Vulnerability: If your phone number is exposed, an attacker could potentially trick your mobile carrier into porting your number to their SIM card (a "SIM swap" attack). With control of your number, they can intercept SMS verification codes for Telegram and other services, potentially gaining access to your accounts.
2FA as a Countermeasure: While Telegram's strong Two-Step Verification (2FA) adds a crucial layer of defense against SIM swaps by requiring a password after the phone code, the initial exposure still creates a significant risk.