Suppose a college-age adult has a vocabulary in English up to the vocabulary of an English-speaker who is 6 years old. This problem makes the ESL student write down the concepts of a little child -- not because she thinks that way in real life, but because she has only a few words to speak with.
It ends up sounding like they are writing a book for kindergarten:
"We like mobile phones because they help us."
But that is not necessary; it's only a bad habit that you can break.
It is far better to at least TRY to write down a sophisticated idea in simple words than it is to allow a simple vocabulary make you write simple ideas.
But that is not the only problem. One of the problems with this essay is that you did not devote any thought at all to making the sentences interesting, lively, balanced. You turned out one dull idea after another, using dull ways to say the obvious. Here is an example I cut and pasted from your first post:
The most advantage of having a mobile phone is you can communicate to your family and your friends no matter what where you are. For instance, you can contact easily to your friends by calling or sending messages everywhere without electricity. It is maybe the main reason why almost all people today choose to own a mobile phone.
> Reduce the word count by deleting the repetition of the same idea.
> You have used all these words to point out that mobile phones are mobile.
With them we can call anyone at any time, independent of a landline connection.
The problem with this passage is not an inadequate vocabulary. The problem is that you have to tell us
1) Cell phones are so great that we all have one
2) And now I will tell everyone why they like having them
You didn't do any work to solve the problem of HOW to write something so obvious and self-evident. It's not about vocabulary at this point.
It's about addressing the problems of composition -- "How oh how can I get away with telling my readers that the sky is blue, or that people like to stay alive, or that they don't want to feel pain, or that we like to breathe air? HOW can I do this without sounding like a 6-year-old?"
I realize that beginners in a foreign language have to produce sentences like "My dog can bark" or "I ride in a car." But you are far beyond that stage now.
In your case, your English is now good enough for you to take seriously the problems of composition.