Adam already knew what Magnus's dangerous but effective method of treatment was. With this method, the Phantom could grow a new limb or even an organ.
It was worth realizing that there was another safer method that Lirla offered, as well, such a treatment was only necessary in exceptional cases.
Usually, even if a Phantom lost an arm or leg, the military or Harvesters would soon take the lost limb from the battlefield, allowing the doctors to reattach it to the body.
Even if the arm was severely damaged, with chunks of flesh torn off or beginning to rot, it was no problem for the doctors working with the Phantoms.
Thus, cases when a Phantom lost a limb completely and needed a new one were quite rare.
Most of the time, it was a consequence of a serious and traumatic battle, so most of the Phantoms in this situation did not mind waiting for the doctors to create a new arm and take a break from Dead Lands.