If you want to give your players more or less cryptic clues abot stuff, you can simply convert statements of plain fact into archaic language. Shakespearian style, or even a bit earlier, like Chaucerian Middle English, depending on how familiar your players are with Shakespearian English. The aim is to have something that they can almost figure out the meaning of just by how the phrases sound, but they're not quite sure if they have the meaning correct or not.
Use something like the Shakespeare Glossary and Thesaurus to find archaic words that don't quite sound like what they mean. Stick them into a riddle or clue, and watch as your players leap to all the wrong conclusions!
Commentary by memnarch (who has not seen the movie)
This feels like a Br'er Rabbit situation, with a side of "heads I win, tails you lose". And I'm not sure if Ben interpreted that line right as well. Sure, the word "fain" looks like it means gladly, but in context of The Tempest scene where the GM got Phasma's lines from, I think it could also mean that she'd prefer to die when it helps the First Order out instead of now. It's almost a shame Phasma's the only one that talks this way; think of the challenge of decoding the intended meanings from the phrases used! Forget Bedoop language, we'll be talking old poetry language!
Killing Phasma still would be the best option at the moment though. While everyone is probably in the same area of the Peace Moon which could mean Kylo Ren finds them quickly, this also means the fleet is arriving very soon and going to cause a big distraction. And metaknowledge also says he might still be throwing a fit over Rey not being found yet while hunting her, so potentially having Phasma's death blip on the Force Sense radar could only help Rey out. Assuming the coffin hasn't trapped her yet, or worse, made a new clone or something of her.
Finn: So. We kill her now?
General Phasma: The wills above be done! But I would fain die a fruitful death.
Chewbacca: Wait! She wants us to kill her.
Zeppo: She does?
Chewbacca: That’s what she just said.
Zeppo: I’m glad you speak incomprehensible gibberish.
Chewbacca: Why would she want that?
Finn: She’s crazy?
Chewbacca: Kylo Ren is Force sensitive. If we kill her maybe he’ll know something is up.
Finn: So... We tie her up! How do you like them apples?
General Phasma: I don’t care. I’m not your mother.
Zeppo: Right, let’s do it!
GM: While you tie up Phasma so Kylo Ren doesn’t get any hint that anything unusual might be happening, let’s cut back to the fleet attacking the Peace Moon...