phone calls go directly to voicemail

You have probably turned on Do Not Disturb. If that's not the case, contact your carrier.

Might you have Settings > Do Not Disturb = "On"?

Do you mean phone calls coming TO you, or phone calls you make to someone else?

Tap settings and make sure airplane mode is off and cellular is on.

Do you see a crescent moon icon at the top of the screen? If so, go to Settings - Do not Disturb = Off.