Welcome to iPhone Forums!
No idea what exactly this means. Sorry!
I have a few suggestions, though, to get rid of this popup.
Which iOS is installed on your device? The latest software is 12.3.1. Update your iPhone, if it’s a different version
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Clear recent contacts. That has to be done in the Phone app, in the Recents tab. Select “Edit” at the top right, then “Clear” at the top left.
Turn off “Network Selection” in Settings - Cellular (or Mobile Data), and turn it on again.
If that doesn’t help, reset your network settings (Settings - General - Reset - Reset Network Settings). This will set back Wi-Fi and cellular settings to default. You’ll have to set those up again afterwards.
Hope that helps.