If you want to begin using the iPhone's speakerphone mode start by selecting Phone from the lower task bar, which is what you select to make phone calls in general. Once you have begun to engage in a phone call you will have a number of different options brought up in front of you, such as viewing the keypad again or putting it on mute. The option in the upper right corner of this box will be speakerphone. You just press this option to activate the iPhone speakerphone function, which will highlight it while it is in use. Once you are done using it during the course of a phone call you can just press it again to turn the speakerphone off.
