Oracle Text

If damage would be dealt to Phytohydra, put that many +1/+1 counters on it instead.

Card Rulings

10/1/2005 If another effect would prevent damage from being dealt to Phytohydra or replace it with something else, Phytohydra’s controller chooses which effect to apply first.
10/1/2005 If Phytohydra blocks or is blocked by a creature with first strike or double strike, Phytohydra will get the counters during the first-strike combat damage step before it deals its own combat damage during the second combat damage step.