Answer:
There are a few ways of writing a phrase for p/3.
1) "The number p divided by 3"
Now, the most accepted way to talk about the result of a division is with the word "quotient", then we can write.
2) "The quotient between a number p and 3"
You also could write it in more "day to day" form, an example of this can be
3) "A third of p, where p is a number"
Where this example may be the most useful in our day to day.