To troubleshoot a phone that is not connecting to the internet over a cellular network, here are a few steps you should consider:

1. Check phone signal strength – ensure there is adequate signal and/or coverage in the area.
2. Make sure the phone is using the most recent software update.
3. Check to see if the phone's network settings have been recently changed or reset.
4. Verify if the APN settings are set correctly.
5. Try connecting with a different carrier.
6. Reset the phone's network to default settings.
7. Toggle airplane mode on/off.