It's an iPhone SE (2020), and Apple have some pretty restrictive App Store rules, but I've found solutions to most situations.
For playtesting the Gamepad implementation I used a 8bitduo SN30 PRO+. The only other hardware used were a pair of headphones (and a charger I guess).
The game engine is (obviously) phaser.
For coding I use the app CodeSandbox. It let's you write nodejs apps, so it works fine with Phaser. It supports git, has a nice extended keyboard layout, supports NPM and includes a browser that can show console.log unlike all other browsers I've tried.
For music I use GarageBand, it's a suprisingly powerful tool.
For sound effects I've tried a few JS ports of BFXR, and the best one I've found is this: https://jfxr.frozenfractal.com
I've finally found a good Vector art app: Vectornator. For pixel art I've used Pixel Studio and Nomad Sculpt (only paid app I think) Nomad Sculpt.
I sometimes use the website ezgif.com for animation and image processing stuff.
The planning is Done in Notion (nice for coop game dev).
My last project was a multiplayer game that had a simple Node process as backend running on a webhotel I rent. The app Termius has a terminal that let me SSH into the server to manage it.
I know some of the apps are iOS only, but android probably have similar solutions.
The hole thing is a bit clunky, but given my current life situation (2 small kids) this is how I can squeeze the most game dev into a day.
The only thing I havn't found a solution for so far is 3d model animation, other than like rotating objects in code.
I'd be happy to go into more details if you have any more questions.