You can use a variable to store the digits in the entry field and when you click another number it concatenates the variable and the number you enter.
Since you enter an integer in the field and we need strings to concatenate we convert them into strings.
We need to use delete as the variable stores whatever is in the entry field for eg. if we click 23 it will show 232 as when you click 2 it stores 2 in the variable and then when you click 3 it prints 23 and 2 because we did not remove the previous 2 that was written there.
This should work:
def inserter(entryblock, num):
digits=entryblock.get()
entryblock.delete(0,END)
entryblock.insert(0, str(digits)+str(num))