Various reports on MLBTR say the Dodgers may or 'may not have matched or almost matched the Cubs' offer, and other teams were around five years, $100 million. I am not gonna fault the Phillies for not going $30 million AAV or six years, either of which would have been required to win this derby.
For sure, he would have made this team better and that would have helped for 2019 moves as well. But at the end of the day you are still selling a 66-win team with a black hole at 3B, a rookie SS and C (plus an entire catching corps that has no history of handling pitchers well), and unproven corner outfielders. If they were gonna go big with someone like Darvish - and convince him to come here - there probably needed to be other improvements. They are not signing anyone to "bargain" contracts because nobody wants to play for the Phillies at a bargain price, and that's going to be true of Lynn/Cobb or Cashner/Vargas/Garcia too.
And the Phillies' own analytics tells them, no matter what the GM or manager says, that the team isn't going to have a shot at 85 wins next season. They do if everyone has best-case scenario years, but you only get there by hoping, not from data.