I have been hearing about iPhone users who for various reasons have lost the full function of their power button especially on the iPhone 5S. Some buttons have either stuck in one place or after being dropped one too may times, taking multiple attempts to use. If that is your case and you really need the power button to close your screen, there is a place on the iPhone that can help you with that. It is called “assistive touch”.
Follow these steps to set up assistive. Go to “settings” and then select “general, “accessibility”. While in “accessibility”, scroll down to “assistive touch”. Turn on “assistive touch”. Click on the home button and you will now see a faint image of a round white icon app that is greyed out. Touch the new app and you will see 6 items that you can click on. If you click on the device icon, you can click the lock screen one and the screen will lock without you having to try your broken power button.
The icon will stay in the background. You can move it anywhere on your screen by a touch and dragging it to the desired spot. This feature is available from the previous IOS7 and is included in the current IOS8. This should help you until you are ready to make that next iPhone purchase plunge.