The first number of such a phone number is called the area code. When calling a neighbor's house, this area code can be omitted. However, when calling far away, you must dial from this area code to get through.
The number that comes after the area code is called the bureau code. This number is also determined by the location. NTT is also the company that decided on this number.
The last four digits of the telephone number. You can choose any number you like. However, if your favorite four-digit number is already in use by someone else, you cannot use that number. In other words, you have to choose your favorite number from a list of numbers that have not been used by anyone else.
When you apply for a telephone, you go to the nearest NTT office. At this time, they will show you a large number of phone numbers. You choose the phone number you want from among them.
The person who chose the number for your home phone number is the person who applied for the phone.