Phil Mickelson just had a remarkable Masters finishing tied 2nd. There was definitely a big change in his physical side having a lost many kilos and looking overall fitter. He commented that he had done a lot of training through the offseason focusing on diet and exercise. He said that this has given him a greater advantage as he's getting older as he can still produce long distance off the tee. Being fitter is also enabling him to not have fatigue spells during the round.
Brandel Chamblee actually made a really good comment. Even though Phil has never had the physical intimidation like Tiger due to not trying to put on bulk muscle, he's managed to prolong his career by avoiding injuries. Brandel also stated the suppleness of his swing compared to Tiger's being very strong, tight and powerful. This suppleness and his mindfulness of protecting his body will likely enable him to still be competitive many years from now. Unlike Tiger who has put himself under physical duress from almost bodybuilder training all those years, is now struggling to put consecutive rounds together.
The breakdown of Phil Mickelson's swing and the reason why it hasn't caused him any injuries, is that he allows the body and the arms to be very free flowing. He has a typical first position where the club head and the arms are in line with each other but the second position he really allows the club to stay low to the body whilst not trying to restrict the backswing. This visual will often mean the club has gone way past parallel at the top of the backswing. He also allows his front foot to slightly lift off the ground to free his body up while turning.
These free flowing moves have been the key to his longevity as he's not trying to restrict any significant movements. He is also quite 'handsy' through the ball with not a great clearing of the hips. He does maintain spine angle and rotate but doesnt try and push the barrier like a lot of swings you see today where they have so much clearance and straighter spine angles.
Phil is one of a kind in what he does but it is proof that a free flowing swing can significantly increase your chances of playing for a long time with limited injuries rather than trying to be more athletic than what you may be capable of.