Panasonic VB-43223 The phone doesn't ring when calls coming from outside

This phone you have is on a Panasonic DBS phone system. The phone system can be programmed to have any combinations of telephones ring under different circumstances. If you can swap phones around (with another known working phone) and the phone at that location still does not ring then it is definitely in the programming for that location not to ring. The phone system would have to be programmed. In that case you would need to get someone (phone system installation company) familiar with the system you have to re-program it. A phone system Programming manual would be required (not a user guide).

This guys wrong. Things like ringer volume should be and usually ARE simple to adjust. When the phone is ringing, simply knock up the volume and there ya go!
The ringer is louder!