Hide your phone number from others using Telegram
By default, when someone joins a Telegram channel their phone number is visible to all others in the channel. This can lead to the person being contacted by, for instance, spammers. Some have been contacted in WhatsApp using the number gleaned from Telegram. The Direct Message facility in Telegram can be used to contact someone without involving their phone number.
The settings in Telegram can be changed to remove the visibility of the phone number.
To make the number not-visible in all your Telegram channels. The steps are almost exactly the same on a phone as a desktop or laptop.
Click the three horizontal lines in the top left of the Telegram window.
Click Privacy and Security
In the Privacy section click the text to the right of Phone number, change the setting to
My contacts depending on who you trust.
You will then see an overview of your setting, and note that there are a few other settings that could also be changed.
There doesn't appear to be a way to make the 'hide number' the default for everyone joining the channel.