It is used to express overwhelming amazement or awe.
Here's a breakdown:
* Increíble: Incredible, amazing
* No: Not
* Tengo: I have
* Palabras: Words
The phrase implies that something is so impressive, beautiful, or shocking that the speaker is speechless and unable to find the words to express their feelings.
Essentially, it's a way to say "I'm blown away!" or "I'm speechless!"