The layout has been getting better and better for smartphone use, and I just want to say thank you to the developers who have been working on this.
I knew that it was possible based on watching Dominion matches on YouTube, that the cards were large enough to tap on. The major outstanding issues for me were clickable options appearing in the play log text, and long-press not showing card details. Now that these things have been fixed, the game is quite playable on my iPhone 6s.