You should be able to configure it in Keybinds.

Patch 2.3 Notes

New options are available in the Keybind interface.

Chat Tab
Reply Temporarily (Forward)
Reply Temporarily (Back)
Switch Chat Mode to Say
Switch Chat Mode to Yell
Switch Chat Mode to Party
Switch Chat Mode to Alliance
Switch Chat Mode to Free Company
Switch Chat Mode to Linkshell (Forward)
Switch Chat Mode to Linkshell (Back)
Switch Chat Mode to Linkshell [1]
Switch Chat Mode to Linkshell [2]
Switch Chat Mode to Linkshell [3]
Switch Chat Mode to Linkshell [4]
Switch Chat Mode to Linkshell [5]
Switch Chat Mode to Linkshell [6]
Switch Chat Mode to Linkshell [7]
Switch Chat Mode to Linkshell [8]