What does the frase "Let's went" mean?

It doesn't make any sense at all. You can say "Let's go" but you can't say "Let's went"

Also, it's spelt phrase not frase

Let's went means Let's go.

Some people think it's funny to use ungrammatical expressions like this. We call such people "sophomoric".

"Let's Went...!" ... was a signature line of "Pancho", the Cisco Kid's trusty side kick on the old TV program, The Cisco Kid...!

Typical "Pancho" quote: "Cisco...'Let's went, before we are dancing at the end of a rope, without music.

You spell that: " Phrase"... not frase.

I think it's an old hipster (bop) phrase, not unlike: "real gone". Plays with time and tense, like the reaction of two hipsters brushed back to the curb by a passing, speeding motorcycle. One saysto the other: "Man I thought he'd NEVER leave!"

It means let's get out of here so fast that by the time I say what i should say (let's go) we are already gone (went).

Great answer!

I have a couple of female friends who live together in a loving relationship. When they mean "Let's go," they say,
"Lesbion our way". It's cute.

I heard Pancho, (The Cisco Kid's partner) saying 'Let's went' well over 60 years ago. I understood it to be a mispronunciation of 'Let's go', the meaning was certainly the same. (Fue/fuimos can mean Go or Went). I have often thought of it and have said it many times myself since. (Funny how it sticks). I did get one funny look from a person some I'm back but simply told them to look up Pancho