The two biggest reasons for this are that the format Commander has specifically blown up in popularity and Wizards of the Coast making a first-party desktop/mob

The two biggest reasons for this are that the format Commander has specifically blown up in popularity and Wizards of the Coast making a first-party desktop/mobile client MtG Arena to compete with games like Hearthstone. Commander is a 4-player casual format that's has as much in common with more typical board games as it does with traditional MtG. Arena is likely what you saw someone playing on their phone. Funnily enough, it doesn't support Commander!