How to delete duplicate records in my database?
I'm assuming that you have no foreign key constraints on the phone column and you have a Primary Key defined:

DELETE FROM foo_schema.bar_table
WHERE primary_key_column NOT IN (SELECT MAX(primary_key_column)
                                        FROM foo_schema.bar_table
                                        GROUP BY phone)


This should group all records by the column phone, and drop all the duplicates but the one with the max PK. Hope that helps. 

Please try this on a dummy table before attempting this on your actual table.