by this way people can add multiple phone no. if some have one it will be just one and someone have five he still can enter. and even normalization rule itself says like that. Means we have to remove the frequency of columns.
There are many situations where we found that two tables can denote to single primary key. I would like to have perfect solution for such stage.
You have three choices then.
Add a teacher id column to the table. Create a constraint that one or both id columns must be populated (only though allow both to be populated if teachers and students can share phones).
Create two phone tables.
Use a sub-type super-type model for students and teachers and relate your phone book to the person entity.
Or just do what most people do and have multiple phone columns for people. Although repeating groups are usually to be avoided most designers don't worry about it when it comes to phones.