If you have something climbable, you should be able to climb it. The game I'm working on now has several climbable objects (tree, vine, walls) and you can certainly climb them when it makes sense to do so. However, you can also go up or down it you're a lazy typist.
If the phone rings, it indicates an incoming call and the natural response is to answer it. But if you want to make an outgoing call you can use verbs like DIAL (if you need to dial a number on an old rotary phone), ENTER (if you need to enter the number on a push-button phone or smart phone) or RING or CALL (if you need to ring someone by name). It's up to you, but try to cover as many bases as possible if you don't want your players to give up in frustration. This is 2020, after all, not 1980.