Cellphone outage affecting Verizon, AT&T, T-Mobile. Here's why your phone says SOS

Tens of thousands of cellphone users were impacted by a nationwide telecommunication outage on Monday morning.

Verizon users were the most impacted, followed by AT&T, T-Mobile and US Cellular users, according to Downdetector.com , a website that monitors real-time outages.

Phoenix was among the most impacted cities, with more than 2,000 Verizon outage reports. The surge in outage reports began at about 6:30 a.m. and continued to increase as of 8 a.m. Arizona time. Downdetector estimates showed more than 37,000 Verizon customers and hundreds from other providers were affected.

The service outage also caused some to see an SOS icon where the cellphone service usually displays on the screen. Here's what it means and how to fix it.

Why does my phone say SOS?

An SOS symbol appeared on the screens of iPhone users who use Verizon where cell service bars are normally shown.

According to Apple support, if you're having trouble with phone service and you see SOS or "SOS only" in the status bar, it means your device can still make emergency calls despite not being connected to a phone network.

The purpose is that you can make calls to first responders in an emergency despite not having cellphone service. When users make an SOS call, the iPhone automatically calls the local emergency number and shares the user's location information with emergency services, according to Apple. In some countries and regions, users might need to choose the service they need.

If you need more help with the outage, you can contact Verizon Support.

If the cellular issue has been solved and you still can't connect to a cellular network, contact Apple support.

This article originally appeared on Arizona Republic: Cellphone outage affecting Verizon, AT&T, T-Mobile. Here's why your phone says SOS