How to Create a Wallpaper Pattern for Your Phone
Once your drawing opens in Illustrator, create a new artboard that is the size of your mobile device screen. Tap on the canvas with the Artboard tool (shift-O) and choose the appropriate Preset option in the Properties panel (for example, iPhone X).
Draw a colored square with no stroke (change Size, Fill, and Stroke settings in the Properties panel).
If your objects are complex, it’s a good idea to group them (command-G or control-G) before duplicating them. This way, you can edit all the duplicates at the same time, simply by selecting one of them and choosing Global Edit in the Properties Panel.
Fill the square with your objects.
When you’re finished filling your square, select and drag both your square and your drawings into your Swatches panel to create a new pattern swatch (Window > Swatches).
Draw a rectangle covering your art board.
Change the rectangle’s Fill option (in the Properties panel) to your new pattern swatch.
Export your wallpaper: File > Export > Export As. Name your artwork, select the PNG format, and select the Use Artboards option. (This way, only the artwork within your Artboard will be exported as a wallpaper.)