Depends on your channel names, each button must have a name that matches in channel distinctively as reported by asterisk. First run autoconfig-buttons-freepbx.sh to see how are your trunk buttons defined, look at the main channel name (in square brackets, and any other channel directives it might have). Then make a call from asterisk and check the channel names in the cli:
asterisk -rx "core show channels concise"
How are the channels named? If the names are all similar, like DAHDI/1-1234, DAHDI/1-2345, then all those calls will be shown on button with channel name DAHDI/1.
Best regards,