If Sanji is still holding Vegapunk then I think the labophase is a red herring and the transmission is originating from Vegapunk’s body.
This would fulfill Sanji’s promise to Kuma since once it’s revealed the whole island would focus on him.
I think this is why there was that clunky chapter where they left Vegapunk only for Sanji to conveniently be alone with him the next chapter.