How do I properly make assets for mobile games

Hi, I’m fairly new with unity and that’ll probably become obvious in a second.

I’m trying to make a mobile game but none of my custom button sprites look right. I made them in Illustrator using a Samsung Galaxy template so that the aspect ratio and everything was correct. Once I exported my buttons as PNGs and put them in unity they looked “okay” but when I ran the game on my phone everything was extremely pixelated. I’m not sure where I went wrong, they don’t look pixelated in the engine preview and the game window.

Also, for clarity, to put my buttons into the game I replaced the sprite of existing buttons and tweaked the Rect Transform.

Edit: I’ve also noticed that if I build my app as an APK and install it on my phone, all of the buttons and text become extremely small.

You’re gonna want to set the canvas scaler to your needs

https://docs.unity3d.com/Manual/script-CanvasScaler.html