rails strip non numeric values before save

The easiest way to do it is by mutating the field= method:

def field=(value)
  super(value.delete('^0-9'))
end

You certainly have defined the phonenumber column as number. That's why when you set '925-555-5555' in the phonenumber attribute, it is casted to a number, and only 925 is kept.

The best solution is to change the type of the column in your database to string. Create a new migration:

change_column :table_name, :phonenumber, :string, limit: 30

Otherwise, you can override the setter like this to remove the non numeric characters (but it won't fix phone numbers starting with '0's):

def phonenumber=(phonenumber)
  write_attribute(:phonenumber, phonenumber.gsub(/\D/, ''))
end

More alternatives in this blog post