My phone is showing no service, what the problem?

Hi Do_That,

Welcome to the Apple Community, where some of us do our best to help each other troubleshoot.

Apple Support has an article online to help you, step by step:

If you see No Service or Searching on your iPhone 

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

Hope this helps :)

See if this applies: https://support.apple.com/iphone-7-no-service