How can I disable guided access without a password on my iphone

Do a reset

Reset: Hold down the Sleep/Wake button and the Home button at the same time for at least ten seconds, until the Apple logo appears. Note: You will not lose any data

See: http://support.apple.com/kb/HT5018

The easiest way is to connect the phone to your computer, click on its name, and click the "Configure Accessibility..." button on the Summary screen.