For Case 1: Using the context of Event > Phone > Phone Ringing
Any call, or those from a specific number, can activate it.
For Case 2: Using the context of State > Phone > Call
If you leave the "Type" as Any," then an active call occurring with the number specified, or any number if blank, will make the Call State context active.
You might use "Incoming" if you do not want the state to activate when you call out.
When the call disconnects, use an exit task.
With state contexts, since you require at least one enter or exit task but do not need to have both, you can separate things into two Profiles or keep them in one as your workflow benefits.
Something here might work for you.