Tap the Speaker icon .
The light bar on the Speaker icon illuminates blue to indicate that the speakerphone is on. If you close the Call screen, the Speaker icon will appear in the Status Bar and the sound from your call is played through the phone’s speaker on the back of the device.
While viewing the in-call screen, you can turn the speakerphone off by tapping the Speaker icon again.
The speaker is turned off automatically when the call ends.
To avoid damage to your hearing, do not hold the phone against your ear when the speakerphone is turned on.