To use the student now has a phone using the phone is invalid because students take the phone in time makes the mistake, and the subsequent impact on performance is reduced.
Using the phone of the student now. A phone usage is incorrect. Students take phone use during class time, making it impossible to study. And the effect was the result of lower classes.
Using the telephone of the students now. The phone is incorrect. Because students cell phones in use class time to never study. And the effect was the effect decreased.