There is no limitation on the number of extensions that can ring on a Pool button. There is a limit of 64 extensions that can have a button for a particular pool.

Make sure the phone is the extension number that you think it is. Press SPKR, dial #00, the display will show you the extension number. Press SPKR again to exit.

You can program the ringing at the telephone itself. Press SPKR, dial #00, press the pool button. The display will show Pool XX-M, where XX is the pool number (probably 70), and M is the ringing Mode, where I is Immediate, D is Delayed, and N is No Ring. To change it, dial *37 for Immediate, *36 for Delayed, or *35 for No Ring.

Make sure the ringer volume is turned up, and possibly turn Abbreviated Ring OFF, so if the phone is off hook, and another call rings in, the phone will ring more than once to alert you of the incoming call.