As for the phone number, you can set up in the Settings > Privacy and Security who and under what conditions can see it.

The Privacy & Security has 2 settings 1) Who can see my phone number - here I can set it to Nobody.

2) Who can find me by my number - here I have only 2 choices - Everybody & My contacts.

What I really want is no one to find me by my number. Even if I have them in my contacts list (the phone contact list). Can I achieve this by not allowing Telegram access to my phone contact list (through app permissions)?

What I want to do is use Telegram only with my userid with people whose number I do not know. Nobody should be able to contact me through my number & nobody should be able to see the link between my userid & my number. By default, what happens is people who have me on their contact list are able to see both my userid & my number together. I want to use telegram totally anonymously - only though userid. Is this possible?