Why does my phone keep showing a black circle loading screen when I put my password in

Check the range of the mobile network, see this Apple article: If you see No Service or Searching on your iPhone or iPad

https://support.apple.com/en-us/HT201415

Check also the Wi-Fi network, see this Apple article: If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network

https://support.apple.com/en-us/HT204051