You are not on call but you do have to be available till a certain time in the am. ( available for work) You are a sub this is how it goes , your hired to cover when needed. if you need off then put in a slip in and get it approved, then you don't have to answer your phone. Not answering you phone in the morning will get you written up, if they call you later , this would be like being on call, you don't have to answer then, you could be anywhere. I never answered my phone after 8 am, went to my other job, you could not get written up for this. And remember a text is not the same as a call,