Here are a few tips
for identifying why your iPhone is not ringing
and how to fix it.
If your phone is in do-not-disturb mode,
incoming calls won't ring
and they'll go straight to voicemail.
When enabled, there's a crescent-moon icon
in your status bar.
Here's how to disable do-not-disturb mode.
Swipe up from the bottom of your home screen.
If the do-not-disturb button,
which looks like a quarter moon, is highlighted,
tap it to disable the feature.
Your phone might think it is sending a ring to a device
that isn't actually connected to the phone.
A potential fix is to enable and disable airplane mode
by tapping the airplane icon in the control center.
To make sure you didn't accidentally block
an important number, open settings.
Tap "Phone."
Tap "Blocked Contacts."
In the list of blocked calls,
see if you've accidentally blocked any numbers.
To unblock it, swipe it to the left and tap "Unblock."
Make sure that your iPhone's ring silent switch
isn't in the silent position.
If it's down with the band of red visible,
it's set to silent
and might've accidentally been bumped into that position.
To test if your iPhone ringer is low,
open settings, then select "Sound & Haptics."
Adjust the volume under "RINGER AND ALERTS."
If the volume is all the way down,
turn it up and see if this fixes the issue.
If all else fails, consider restarting your iPhone.
This is a last-resort step
when your iPhone runs into software problems.
If none of the other troubleshooting tricks
solved your problem,
you probably have a hardware problem with your iPhone,
like a damaged speaker or a fried port.
You can go to Apple's support page
and set up a Genius Bar appointment
to have someone look at it in person.