It was 30 mins for required password timeout that I set few months ago. Yesterday I noticed that phone got locked each 3 minutes and required password settings has only 4 options (each time, 30 sec, 1 min, 3 min). How does this thing happened. Is there any way to get my previous settings?
It sounds like your company enforces a security policy on devices that are connected - you may see that the option to turn the password off is also disabled. This is the case with my employer's connection, although they allow up to 5 minutes before requiring a password.
If you remove your work email account, you should see the restrictions lifted until you add it back.
If you think three minutes is a little over cautious, then you need to speak to your IT department, and make the case to get it extended.