For everyone playing dota 2 and playing ranked:
http://blog.dota2.com/2017/04/matchmaking-update/
There will be a two-week grace period from today during which players have time to register a number, but starting on May 4th, accounts without a registered number will no longer be eligible for Ranked play.
Keep that in mind!
edit: oh i misinterpret: you cant play ranked anymore if you havent registered a phone number but you can still register a phone number after those 2 weeks.