Make Sure You Actually CAN Make a Phone Call
The first thing you need to make sure of before you start trying to fix your iPhone is that you’re allowed to make phone calls. That means checking your mobile plan to make sure you have enough minutes available and that outbound calling hasn’t been blocked on your account for some other reason.
Also, make sure that you’ve paid your bill. If you didn’t, your service provider might have cut your service off without you knowing about it. Some providers will cut off your ability to make voice calls before they turn off your cellular data.
The second thing you need to check is your iPhone’s signal. Maybe your iPhone doesn’t have good reception where you are right now. You can check your reception by looking at the number of bars in the top right corner of your iPhone. Usually, you’ll want to have three or four bars to make phone calls, although this can depend on your network and whether you’re on 5G or LTE.