The deadline to do so was today. Werth has until November 30th to accept or decline.
That would lead to a hearing to be held to determine his salary for one year with the Phillies.
It would then open the door for negotiations for a long-term deal.
If he declines, the Phillies will be compensated with draft picks should he sign with another team.
This is a last-ditch effort to keep Werth. He is considered to be on of the highest rated free agents on the market.
Meanwhile, the Phillies on Tuesday decided not to offer arbitration to reliever Chad Durbin.