Why is 上 after 桌子 and not before?
在......上/下/里/外 refers to a state of being , it's a phrase
If you use it that way, it means the cellphone is "getting onto the table".
Does this sentence need the 在?
You can omit the "zi" but not the "zai".
Yeah it's necessary.
Why don't they accept: 你的手机在桌子上边。 ？
If you say that in China, most people will get what you mean, but no one talks like that. Native speaker here. I'm just here for character recognition.
That would be like saying the phone is above the table, on the top side. Instead the phone is sitting on top of the table.