How to hear phone rings when phone automatically locks and Do Not Disturb setting can't be unchecked?

Hello:

The problem is that I'm not hearing my phone ring.

The Do Not Disturb setting has two "options" under SILENCE: Always and Only while IPhone is locked. The second "option," Only while iPhone is checked. I put the word, options in quotes because I did not check, Only while iPhone is locked. I cannot uncheck it. I believe that I do not want either option checked. Moreover, underlying of the symptom of not hearing the phone ring is that the phone automatically goes into lock mode after a few seconds.

The iPhone was purchased last March, 2013.

With thanks in advance for advice and recommendations.