The old school roguelikes that were built when they could count on a keyboard all have heavy keyboard dependencies. Nethack and Angband both have command sets that extend beyond the case-sensitive letters. (Protip: When forgetting what letter a given command is, do not just start hitting keys looking for it!) Of course you tend to use a subset in play, but even that subset can be quite large.

If you want to play a roguelike on a portable, you'll need to play something built for portable. I have no specific recommendations... unfortunately, I can't help but compare things to Angband (my drug of choice) and everything ends up too simple by comparison. That's just my problem, though. Android certainly has a lot of roguelike things on it, the Web is full of reviews and recommendations: https://www.google.com/search?q=best+android+roguelike

I've ascended in an Android Nethack port before. I think it was this one: https://play.google.com/store/apps/details?id=com.tbd.NetHac...

WazHack. It is not nethack, but is a very well-done derivative of it.

I play, enjoy, and have ascended in gurr's Android Nethack. I find it has a really natural interface, although it's certainly different from terminal. https://play.google.com/store/apps/details?id=com.tbd.NetHac...

Try out Pixel Dungeon. It's great.

Have to say the Android versions all seem pretty unplayable.

Take a subnotebook on the train!

Subnotebook? That word is almost as old as NetHack :-)

Subnotebooks are almost as cheap as Nethack. A no-brainer for sure!