OK first off... take a deep breath and relax. When I was getting ready to leave for Maternity leave with my son my co worker was just fine with learning things on her own. I however was not comfortable with that. I made a manual of my job duties. Did not tell anyone. The day I went on leave ( I was being disabled early because of back issues) I simply set it on my bosses desk and told him that anything they may need to know is there.
Now, my job was not nearly as complicated as your sounds, but there were things that I did that no one knew I did. They just got magically done. That could be an option. It is not your resposibilty to make sure your boss trains someone on your tasks. That is his.her responsibilty. If they choose to not have someone shadow you, that is his/her fault.
As far as the phone calls. Don't answer the phone if you don't want to. If you choose to call them back, WHEN IT IS CONVENIENT FOR YOU AND BABY, then so be it. I would not go out of your way. Procrastination on their part does not constitute an emergency on yours. You are protected by FMLA laws, so if they threaten you with your job, you have a leg to stand on and a lawyer would be more than happy to take your case.
I would continue to give gentle reminders and even say something to your HR department, that way it is documented that you have suggested someone be trained on your duties so you can recover at home with out worry.
Hope that helps, but so keep in mind you have laws that protect you and it is not your fault or responsibility.