Compare Field Data To Entire DB

I have a page that adds data to an Access DB. When an employee adds a record I want to compare the phone number from the data they inputted to all of the phone numbers that are currently in the database for that field.

If the new phone number currently matches any record in the DB I want to have an alert that notifies the employee that a record with that phone number exists with the date that the first record was inputted and ask whether they want to continue and add the the new record or cancel the addition of the new record. Otherwise, I want the data to just be added. At this point I have a Case statement that will add the record after a submit button click.