What is the verbatim meaning of the phrase 了不得了?
It's rare to use "了不得了" in Chinese, but using "不得了了"(Bu4 De2 Liao3 Le0) is more common.

So, "不得了"(Bu4 De2 Liao3) means that cannot be ignored and even extremely serious/important. The "了"(Le0) at last does not have any real meaning but just a short pause of the phrase.

It's proper to say "不得了了, 您儿子被蛇吃了!"

The verbatim meaning of the sentence above:


  It can't be ignored that, your son have been eaten by a snake.


Be careful don't confuse "不得了"(Bu4 De2 Liao3) with "不得了"(Bu4 De2 Le0) and "得了"(De2 Le0) and "了不得"(Liao3 Bu4 De2).