The Phas3r is evolved by levelling it to max level and with the Empty Tome item. I found that the level has very few chests overall, so if going for this it may be worth leaving a chest until you’ve met the requirements to evolve the weapon.
The Phas3r is a pickup in the “Space 54” level.
The Empty Tome can be picked up 5 times in the “Space 54” level allowing you to immediately level it to max.