Phone not connecting to wifi .

Hello Cbmom28,

Welcome to Apple Support Communities. 

We understand that you’re not able to connect to Wi-Fi on your iPhone 12. We are happy to help.

These steps may help. Please use the steps here to restart your iPhone: Restart your iPhone - Apple Support

"How to restart your iPhone X, 11, 12, 13, or later

1. Press and hold either volume button and the side button until the power-off slider appears.
2. Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
3. To turn your device back on, press and hold the side button (on the right side of your iPhone) until you see the Apple logo."

Apple recommends these settings for your router: Recommended settings for Wi-Fi routers and access points - Apple Support

"Router settings

To ensure that your devices can connect securely and reliably to your network, apply these settings consistently to each Wi-Fi router and access point, and to each band of a dual-band, tri-band, or other multiband router. Before changing the settings, you should take these steps:

• Back up your existing settings, in case you need to restore them.
• Install the latest firmware updates for your router. This is generally done from the app or webpage that you use to administer the router.
• Update the software on your other devices, such as on your Mac and on your iPhone or iPad, to ensure that they have the latest security updates and work best with each other.

After changing the settings, you might need to forget the network on each device that previously joined the network. This ensures that the device uses the router's new settings when rejoining the network."

Please use the steps here to check for potential wireless interference: Resolve Wi-Fi and Bluetooth issues caused by wireless interference - Apple Support

"How to reduce wireless interference

These general steps can help achieve a cleaner, stronger wireless signal:

• Bring your Wi-Fi device closer to your Wi-Fi router. Bring the Bluetooth devices that are connecting to each other closer together. 
• Avoid using your wireless devices near common sources of interference, such as power cables, microwave ovens, fluorescent lights, wireless video cameras, and cordless phones.
• Reduce the number of active devices that use the same wireless frequency band. Both Bluetooth and Wi-Fi devices use the 2.4 GHz band, but many Wi-Fi devices can use the 5 GHz band instead. If your Wi-Fi router supports both bands, it might help to connect more of your Wi-Fi devices to the 5GHz band. Some dual-band routers manage this for you automatically.
• Configure your Wi-Fi router to use a different Wi-Fi channel, or have it scan for the channel with the least interference. Most routers perform this scan automatically on startup or when reset.

If you're using USB 3 or Thunderbolt 3 devices with your computer, you can limit their potential to interfere with nearby wireless devices:

• Use a high-quality, shielded USB or Thunderbolt 3 cable with each device.
• Move your USB 3 or Thunderbolt 3 devices—including any USB hubs—farther away from your wireless devices.
• Avoid placing USB 3 or Thunderbolt 3 devices on top of your Mac.
• Turn off any USB 3 devices that aren't in use."

Let us know if you have further questions.

Take care.