phone varchar(15) NOT NULL UNIQUE,
-- Here is a good column for phone number with datatype varchar(15)
phone varchar(10) NOT NULL UNIQUE
Phone number can be INT and also you type as varchar
You can use char(15) i would use 15 instead of 10 as some international numbers can be up to 15 digits
Or you could use Varchar(19) to cater for other characters and country codes e.g. +123 etc...