A Dashboard, including on a phone screen, is certainly a powerful alternative to a button device if you can find a way to mount and power the device! I think that's a good, creative idea.
If you do want actual button/remote devices, I live in the US and can think of several good options, but I'm sure the options are more limited in Australia. For example, can you find the Lutron Smart Bridge Pro (L-BDGPRO2-WH) and Lutron Pico remotes? In the US, the bridge is a bit pricey, but the remotes are cheap and easily mountable standalone or in standard US-sized rocker/decorator-style wall plates (one of two common light switch styles, though these don't look much like any of them besides size). The Eria Dimmer remote costs a bit more than the Pico remotes, but it's standard Zigbee and doesn't need an extra bridge or anything to make it work. The Hue Dimmer remote is similar but costs a bit more and doesn't match a standard US switch size (so can't be mounted exactly like one), but I suspect none of these would match Australian switches anyway.
Aeotec does have a few Z-Wave remote devices that I haven't used, but they do look nice. In the US, they're more expensive than other alternatives, which is mostly what has deterred me from them. The Osram 4-button dimmer is Zigbee, a bit smaller and less cute but often found for super-cheap (I got two for under $10 USD a while back).
For a list of button-type devices that work with Hubitat, this list/thread may be helpful: Hubitat Elevation supported button controller capabilities matrix (but again, I have no idea how easy some of these are to find in Australia).
But back to your phone/tablet idea, there are also some threads about how to make that work if you want, especially if you search the SmartThings forums. Most of these are probably US users, but I know some put a recessed outlet behind with a USB port and power the device, mounted on or nearly flush with the wall, that way. What you can do depends on the depth of your recessed outlet (and size of the power brick if you have one). My eventual plan is to put a recessed outlet box in one of my hallway walls that will be used for just low-voltage, a PoE plus USB-charging insert I found and am hoping to use to connect directly to a wall-mounted tablet with a flat, right-angle USB cable inside a cased tablet and hopefully not be able to see anything besides the case and tablet.
...but that's a lot more work than I've felt like doing at home lately, so it's a "some day..." project for me. 
