For everyone complaining about no phone support:
With the UI as it is now, some things would be nearly impossible to use on a smaller screen. Sure, the actual gameplay would be fine, but have fun trying to set up your decks on a 4-5" screen. It's a bit of a mess even on my LG G Pad 8.3, I can't even imagine trying it on a smaller screen than that.
Also, it seems to be pretty unoptimized. The menus lag quite a bit on my G Pad.
Works totally fine on larger phones though, made a deck with no issues on a Note 4, even uses the stylus fine (which I didn't use when making the deck, just tested it once in a match earlier). It feels fine for using with your fingers normally too, played a bunch of matches.
I'd say menus are a little slow (15-20fps), but not horrible, especially considering they're menus and you don't need to use them too much, but the game itself runs better, not 60fps smooth, but somewhere between 20-30fps, which is totally playable, even for me being used to 60fps from a PC.
I do agree smaller phones probably have more of an issue for deck building (they'd probably manage playing fine), but on the larger ones it works fine as is. I'm not even sure I'd want to use a mobile client on my phone, if there were hurdles added to it to make it more accessible vs the regular one.
As for the optimization, I definitely feel Android is just being Android, generally things just don't run as well on Android as they do on iOS, and that's just how it is I suppose.