Phrasal verbs – call

call for means collect somebody. Example: I will call for you at 7 pm. Second meaning require. Example: This calls for a celebration. Third meaning is demand. Example: The MP called for an investigation.
call off means to cancel something. Example: The meeting was called off by the manager.
call on means to visit somebody. Example: Jane called on Mary while she was in hospital. Second meaning is turn to someone for help. Example: John called on his friends for support.