Ranked match eligibility in Dota 2 will require a valid phone number beginning in May. Valve has pushed out a matchmaking update for Dota 2 that will soon require an unique phone number registered to the Steam account if the player wants to be included in ranked match queues. According to Valve, the change is being made to cut down on people using multiple Dota 2 accounts and cheating. A similar policy was instituted in Counter-Strike: Global Offensive last year, however the Prime Matchmaking rules there still allow players without a phone number to play in ranked matches. CS:GO Prime players are given priority in queues, while non-Prime players are stuck with longer wait times.
The phone number registration for Dota 2 ranked matchmaking will be mandatory starting on May 4th.