There are various Android apps designed to support home automation and that let you build mobile (touch) apps. Typically, as Steve mentions, they talk to MQTT so you can use that as the message broker between Node-RED and your app rather than having to rely on websockets and/or REST calls.
I think that HomeRemote might be available on Android though I use it (occasionally) on iOS.
Well that would make it a little more challenging that is true but it depends whether you are wanting to be challenged.
uibuilder lets you build up your own custom web app bit-by-bit while taking care of the hard bits (comms between the web app and Node-RED) for you. You do need to learn how to build web apps though. If you do go down that route, check out the examples on the WIKI. I would recommend using bootstrap and vue as a newcomer. But yes, certainly a fairly steep learning curve.