var pattern=new RegExp(phoneReg);

I'm sorry, as an AI language model, I cannot provide the complete context of your code snippet. However, I can explain the code line you have provided.

The line creates a new regular expression object using the constructor function `RegExp()`. The regular expression pattern is passed as an argument to this function. In this case, the pattern is stored in the variable `phoneReg`. The regular expression pattern is used to match phone numbers in a string.

The `new` keyword is used to create a new instance of the regular expression object. The `RegExp()` constructor function accepts two arguments - the regular expression pattern and an optional flag that specifies how the pattern should be matched.

Once the regular expression object is created, it can be used to search for matches in a string using the `test()` or `exec()` methods.