(If you're unsure of your Mac's resolution, please refer to this tutorial.)
1024 x 768
1280 x 800
1280 x 1024
1366 x 768
1920 x 1080
2560 x 1440
(Refer to this tutorial to find out how to change your iPhone wallpaper)
iPhone 4 (all models)
iPhone 5 (all models)
iPhone 6 (not 6+)
iPhone 6+, Samsung Galaxy S4 and S5