Most phones and tablets have this option built in. For Androids, put your cursor in the comment box and when your keyboard appears there should be a keyboard icon (usually in the bottom right hand corner of your screen)
Click this and then choose 'Google Voice Typing'. This screen will appear:
Tap to speak and you should find that what you say is typed up for you.
On an iOS device put your cursor in the comment box and when your keyboard appears there should be a microphone icon:
Enable dictation and begin speaking.
Please always check what has been entered in the comment boxes as your phone may not have always heard you correctly!