20-G-4-b Notwithstanding the assignment window
provision of this sub-paragraph 20-G-4, above, a pilot
assigned to fly a schedule who has been on sick leave
shall be entitled to fly his scheduled trip only if he advises
the crew desk fourteen (14) or more hours prior to the
scheduled departure of the trip that he has obtained or
plans to obtain his return to work medical release.
As far as I know, this is the only way a trip can be taken and given to a line holder. I never had it happen to me. The line holder does not have the ability to take a trip away from a reserve because they like it better than the one they have. All trips remain in open time until 28 hrs prior(48 hrs for intl trips) for line holders, so if a line holder wanted the trip and was able to swap, they would have been able to pick it up prior to it being available to reserves.
I would say that as a reserve, you could often end up with better flying as a reserve picking up trips than you could as a junior line holder flying the sh-t schedules that pbs spits out.
As far as phone availablility, once you pick up or are assigned a trip, you have no obligation to answer the phone. They will try to "give you a head up about your schedule". You don't have to take the call or return the message, just show up in ops at the required time.