PLEASE STOP OFFERING THIS ADVICE.
Increasing your WAP broadcast power does nothing to improve signal in the other direction, so while it will make your mobile devices show more bars, it won't actually improve network performance. TCP doesn't work unless a host can both send and receive (packets need to be ACKed), so even if the client receives further away from the WAP, it'll stop getting new packets if it can't notify the sender that those packets were received.
All that really happens when you increase broadcast power is an increase in interference with neighboring WAPs, which tends to lead other people to the conclusion that they also need to increase broadcast power in order to overcome the interference that you created.
... so you're suggesting you turn up the power on BOTH ends?