I thought about an app version a few times. The options aren't great though.
The most obvious option is a PWA, progressive web app. This is basically just like saving a webpage on your phone home screen. It would be like a regular browser window, but no address bar or other usual browser features. It would just be the plain mobile version of the website plopped in a window. This would be really easy to implement, just really lame too, less features than a regular browser window.
The next easiest to do would be a native app wrapped around the website. This is similar to the PWA, but with slightly more possible features since it's an app - just with the actual browser-game loading "inside the app". It would kind of be like a "thardferr browser" where it can do a bunch of things like a normal app, and like a normal browser (chrome, etc), but the only website it can load is thardferr, and the only features we could add wouldn't be connected to the game in any way. This is probably the best option since it's kind of a middle of the road approach, but the quality wouldn't be any better than the existing mobile version, and it would probably feel pretty clunky going between the game and other app features.
The other option is a full native app. This would be totally rebuilding the game from scratch, but specifically for phones. The nice part about it is everything would look and feel perfect on phone, and we could build unlimited kinds of features for it and they'd all flow together really nicely. The only downside to this is cost, just to start would be around 500 dev hours, plus maybe another 100-200 on top of that for debugging to get to where we are now with the existing game. Any changes we did in the regular game would be an extra 3-4X multiplication of dev time to also update the apps (assuming we did android and also iphone).
I would much prefer doing the native apps, if we had the time or funding, we could do some really fun stuff with native apps. Time to make a GoFundMe I guess lol