Hello, I wanted to start speedrunning this game, and I was wondering if I could get a tutorial on how to open the game after you download its file?

After downloading the file, open the file in the downloads folder. Then press install

Would it be possible to download the game on a phone?

Yes. I have the play store link

https://play.google.com/store/apps/details?id=com.frojo.moy.platformer.android

Is there a way to download the game on iOS?

Unfortunately, I haven't found an iOS alternative yet.