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a phone number, despite being called a number, isn't an integer. it is a formatted string consisting of 3 or 4 fields, depending on which country you live in and if you are including the country code with international numbers. the signed integer you are using (int(12) isn't even valid) can only hold a value up to 2147483647 (214 748 3647) which can only store some US phone numbers up to area-code 214. use a string data type and format the value into a common format before using it. once you define the column with a usable data type and as a unique index, just attempt to insert the data and detect if a duplicate index error number occurred to determine if the phone number already exists.