Panasonic cordless phones give you the option of raising and lowering the volume of the receiver's ringer. The ringer is actually an audio clip that plays every time you receive an incoming call, alerting you that somebody wants to get in touch with you. There is a chance you might accidentally press a combination of keys and lower the ringer's volume to zero. If that is the case, you can easily reverse it to get the phone ringing again.
Take the phone off its cradle.
Wait a second or two for the phone screen to light up.
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Press the "Volume Up" key until you see the words "Ringer On" on the phone screen. This will indicate that the ringer has been enabled.