(updated post) The Nekogram telegram client contains code that grabs your Telegram ID and phone number to send to their own bots, also some other OSINT bots mentioned. They admitted to it in their channel (@NekoUpdates) and are insulting users in the comments. Assume your number and user can be correlated at a worst case. Keep away from third party clients.

https://github.com/Nekogram/Nekogram/issues/336

https://github.com/RomashkaTea/nekogram-proof-of-logging