From my knowledge, Ralstonia Eutrophus produce PHB in a carbon rich environment as a fat storage molecule as a response to physiological stress. Therefore I would assume it would be produced, stored externally and then used by Ralstonia Eutrophus when they are lacking carbon and thus retrieving it would be easy as it is external from the bacteria.
I'm not 100% but this is just what I can deduce from what I know.
When Alcaligenes eutrophus is used to produce this plastic, the extraction involves the breaking down of the bacteria's cells walls and separating this from the cell debris.
Are you sure, I know Biopol is removed from the bacteria by dissolving it in trichloromethan or chloroform, but are you sure it is the same for PHB alone.