Hello geofd,
Thanks for asking the Apple Support Communities for help with your Phone reception.
1. Please start with the troubleshooting in this help article. Even if you have a small signal, the steps are still valid: If you see No Service or Searching on your iPhone or iPad - Apple Support
2. Also verify if there is an update for the carrier settings on your device: Update your carrier settings on your iPhone or iPad - Apple Support
3. Remove any cases and test without the case to see if the issue is occurring without the case.
4. Navigate to Setting > Mobile data > Network Selection > Change to Automatic. Does the issue persist? (If the setting is already set to Automatic please try to change to Manual and select preferred carrier.)
5. Are you experiencing this in certain areas? Please check for interference and see if moving to another area has the same issues: Resolve Wi-Fi and Bluetooth issues caused by wireless interference - Apple Support
The article above also recommends contacting your provider to see if there are issue with the account. If you still have issues after all these steps, please let us know and we will provide what we can to continue troubleshooting this with you. Thanks and have a wonderful day.