itch.io

Unfortunately, about making a phone game niche like this game and other's, there will be near-to zero references to it, nor a template existing for it. This genre's extremely niche, and to top it off, most dev's wouldn't share open source codes that would allow people to just copy paste their scripts and nodes, but here are some of the learning resources that I know:
1. https://gdscript.com
2. https://docs.godotengine.org/en/stable/index.html

I'm not really sure how solid is your foundation is in programming cores, but if you have a solid grasp towards conditional statements and loops you should have an easier time learning the resources from those links.

additionally here's a tip on what I do, and probably what most probably do, I simply make a scene and attach a photo or image towards it, and there we have a simple background, for the resolution, you should be able to adjust it on the project.godot file. As for the icons on how I do it and probably others too, they just make a simple 2d object, overlay it with an image, then attach some kind of clicking event handler which switches to a different scene if it gets clicked. I hope that helps.

Here's also my bonus recommended roadmap:

1. Introduction to Godot & GDScript
2. Variables, Data Types & Operators
3. Functions
4. Conditional Statements (if, elif, else)
5. Loops (for, while)
6. Arrays & Dictionaries
7. Classes, Inheritance and Node System
8. Scene Structure & Script lifecycle (_ready(), _process())
9. Signals & Communication Between Nodes (this is where the icon thingy I told you comes in)
10. Input Handling
11. Timers & Game Loop logic
12. Basic Physics & Collision detection