outside (a region, area, etc.); out of range (of a mobile network, radar, etc.); outside the sphere (of influence, etc.); out of contention; out of reach
山の中で圏外になった。
I went out of range in the mountains.
圏外で電話が使えなかった。
I couldn't use my phone out of range.
地下は圏外になることが多い。
Underground often has no signal.