This is definitely a strange trade. IMO Crawford probably has more trade value than Segura because of the age and Segura's salary. He has retained most of his prospect value and I believe Seattle thinks he will be as good as Segura. Even if they don't think he is quite as good, getting rid of $60 million in salary commitments is important to them.
While it is a plus for the Phillies to include Santana in a deal, it also removes the opportunity for them to buy a prospect in a Santana trade (with reduced salary). So maybe the Phillies are insistent on that piece. More likely I suspect we'll get a reliever or two with mid-level salaries. We'd be doing Seattle a huge favor by taking Juan Nicasio or Mark Rzepczynski. So if we got one of them we would deserve a pitching prospect also in the deal.
This is a deal that helps the Phillies short term (Hoskins to 1B, Segura probably for a year or two is better than Crawford) but hurts us long term and diminishes our financial flexibility in 3-4 years. Not fatal of course as we could always be a luxury tax team, but if we added Machado/Harper and a left-handed starter and a closer and then started paying Nola and others big bucks the extra money for Segura could hurt.