converting phone number into phone 'word' - python

I want to convert given phone number into respective letters

0 -> 'a'
1 -> 'b'
2 -> 'c' etc.

E.g. the number 210344222 should get converted to the string 'cbadeeccc'. I understand my return is wrong at the end which is where I am stuck, so can you please explain how I would instead return the letter conversions.

def phone(x):
    """
    >>> phone(22)
    'cc'
    >>> phone(1403)
    'bead'
    """
    result = "" 
    x = str(x)
    for ch in x: 
        if x == 0:
            print('a')
        elif x == 1:
            print('b')
        elif x == 3:
            print('c')
    return result