I'd like to note that identifiers like passport number, phone number, or a credit card number, are not really numbers (despite the word "number"). Number is something the represents a quantity (for example, 3.5 km). Credit card number or phone number is not a quantity, it is just an identifier, a string made of digits. For example, there are phone numbers that start with zero (like 02), and the leading zeros would be lost if you try to convert it into an integer.

So if you need a database field or a variable for such identifier, you should choose a string type, not numeric.