**UPDATE** "At A Loss For Words" is what I submitted. I believe it's correct ;)
It took a while because I assumed it was an idiom and couldn't get "Cat Got Your Tongue" out of my mind. Turns out it was a simple phrase. My hint, for those interested in solving it, is "misplaced lanaguage". In case you forgot the puzle, here it is again:
Q: Think of a familiar phrase in five words that means 'tongue tied.' One word in it has one letter, one word has two letters, one has three, one has four and one has five — though not necessarily in that order. What is the phrase?
I will leave more hints for those who leave a comment ;)