Just to go the other way: if you do want to actually remove the verb, you should be able to do something like this:
list remove (telephone.displayverbs, "Pick up")
The exact spelling of the verb (including case) is critical.
I'm assuming the telephone is in the room, not in the player's inventory. (I didn't quite understand when you said, "Since "pick up" clashes with the take(Or whatever it was) verb, the script is under "Inventory" in the object.") If the verb shows up when in the inventory, use "inventoryverbs" instead of "displayverbs".
(Note: I haven't tested this code.)