Company demands we answer our personal phones on our days off when they want to call us in to work

I read this in the 85 page handbook after I started.

This is a large security company in the United States. I am an hourly employee working a 12:30p-830p shift with no breaks (yes, it's legal in PA).

However, the shift before me (4:30a-12:30p) was just fired due to sleeping in his car. He was fired on Friday.

My supervisor came into work and told me they expect me to cover some hours of his shift this week while they replace him. Someone else from my company mentioned that if they call me in to work, I absolutely must answer. I can not ignore their calls or texts. I consider this ridiculous as I don't even get home until 9:30 at night and sometimes go to bed at 1am.

So, they're going to be calling me at 5 or 6am trying to get me to come in because THEY don't have enough coverage and if I don't pick up it's on me. Also, in the handbook it clearly states if I block any of their numbers, it's an immediate termination.

Thoughts on this?