Maybe this has been around for a while but when placing a phone call with Siri, you can ask her (or him) to also turn the loud speaker on.
This is particularly useful when making handsfree phone calls in the car. Especially if you’re phone is plugged in as you can also use the ‘Hey Siri’ command. That way you don’t even need to tap the home button.
To make a phone call with speakerphone turned on simply say something along the lines of…
“Hey Siri, Call Craig using speaker”
You may also be more specific…
“Hey Siri, Call Alex at home using speaker”
Update: ‘Hey Siri’ requires iOS 8.3 or later.