If you anonymise coins then why worry about kyc in past? Does joinmarket still works?

The authorities will still know when you purchased and how many. In addition, you will not be able to prove you've sold any/all your stash.

I know I’ll definitely regret giving you my phone number

You don’t give us your phone number or your contacts. Everything is done client side. We don’t touch Bitcoin and we don’t touch fiat. We have no records of trades. We have no records of anything. We simply connect you with your friends and friends of friends who are interested in trading with Bitcoin.