Use Speakerphone - Brigadier™ by Kyocera

Note The speakerphone is only be available while on a call. Once the call is ended the speakerphone is disabled.

While on a call, tap the Speaker ON switch Speakerphone On iconn (at the lower-left) to enable or Speaker OFF switch Speakerphone Off iconn (at the lower-left) to disable the speakerphone.
Note You enable it when you see a blue line.