Phalaris is pretty fibrous so you'd probably clog up your blender. Chop it up with scissors and simmer it in distilled water for a while. Strain out the solids, reserving the tea, and maybe cook them in a fresh lot of water again. Strain and combine both brews and you can proceed with adding base, naphtha pulls, etc. If it's just some random phalaris that you've picked, be prepared to be disappointed with the results.

Another method is to put the (fresh) grass through a wheat grass juicer. After pressing it a couple of times, the pulp can also be brewed in water as before. Beyond that, there are tons of phalaris preparation resources around here that can be found with a bit of digging about in the forums and the wiki. There's one particular document that I'll try and find in order to link it here.