I was in seat 13F today on 2196 ATL-SAT. After we taxiied onto the runway, the person sitting in 13Es phone started ringing. The FA in the jump seat next to him did not say anything. Shouldn't they at least remind him that it is supposed to be in airplane mode, instead of just ignoring it? Also, the same FA was not in the jumpseat for landing. Is that a requirement or can they be in any jump seat for landing?