Scared of being fired, or getting less hours?

I work casual, and am also on call, usually when someone calls in sick or can't make it for another reasons I'm always fine with coming in and taking that shift, so I think that's why my boss always asks me first, but I broke my iPhone by accidentally dropping it from my car yesterday and it completely smashed and lines started apparently on the screen too so I couldn't see anything, and went to get fix today because I got paid today so had enough money to do it, and did that about 11-12pm and they fixed it after a bit after that, but because it was 30 mins from where I live and was had no battery so I didn't even think if I had gotten any messages, until I got home and charged it I got a missed call from my boss asking me to work at 5am and then 8am it said she sent the message, but I didn't have access to my phone and obviously couldn't get back to her, or anything. I'm supposed to have yesterday, today and tomorrow off work, and I don't want her to feel like I'm making excuses and fire me or give me less hours because of this, so do you think if I told her what happened she'll understand? Like i was stupid to have dropped my phone yes, but there wasn't much I could of done until today

Since you usually come to work when they call, and you didn't even answer the phone, your boss will probably understand that you couldn't. In the future, you should find some way to contact them in case your phone breaks.

Just phone her and tell her what happened. Offer to work if you are needed

Then call and tell her

MOST employers understand that this type of thing happens and won't hold it against you if you can't be reached ONCE to work a shift you were not previously scheduled to work. If they do, it usually means they were already looking for something to cite as a reason to get rid of you, which doesn't seem to apply in this case.
I would recommend calling and telling them you didn't get the message before because your phone was being rwpaired.