Explode Phone Number (Python!)

Wahoo! I wrote my first python script that does something. It extracts a phone number out of a string… and divides it up into an array.

def extract_phone_number(number):
    phone_number = ''
    for index in range(len(number)):
        if number[index].isdigit():
            phone_number += number[index]
    
    return [[phone_number.zfill(12)[-12:-10]], 
            [phone_number.zfill(12)[-10:-7]], 
            [phone_number[-7:-4]], 
            [phone_number[-4:None]]]

Use it like this…

extract_phone_number("512-555-3012")
extract_phone_number("11 512 555 3012")
extract_phone_number("5553012")

Anybody that knows python: Am I doing this right, or am I missing something obvious?