Zoom doesn't have a recommended background size for Android or iOS users, but since it should fit your vertical screen, a standard phone wallpaper size of 640x960 pixels can help your Zoom background fit nice and snug.
How to make your own funny Zoom backgrounds. Use this funny Zoom background to get some laughs-and lightly tease the people whose laughs you actually hear. No matter how masterful we get at using Zoom, it seems like there's always one person who forgets to mute their audio on large conference calls.