You need to make settings on the printer to only use staple finisher-P2 when faxing.
Tap Settings > General Settings > Printer Settings > Output: Fax, and then select Finisher Tray.
When copying, printing from a memory device, and so on, from the printer:
There is only an output tray when staple finisher-P2 is installed. You can only select Finisher Tray.
When printing from a computer:
There is only an output tray when staple finisher-P2 is installed. If you select Auto Select or Face Down Tray from the Output Tray menu in the printer driver, the paper is output to the finisher tray. Depending on the type of printer driver being used, you may not be able to select Face Down Tray.
When using the finisher tray, do not remove your printouts while the print job is still in progress. The print position may be misaligned and the staple position may move from its original position.