Why is my Iphone 5 NOT ringing if somebody call me and Missing Ringtones ?

Hello there, Thuy Loan.

The following Knowledge Base article offers some basics to review for the issue you're describing:

iPhone: No ring or sound from built-in speaker

http://support.apple.com/kb/TS1205

and

Phone - Learn more about iOS 7 and iPhone - Apple Support

http://support.apple.com/kb/index?page=tidetail&product=iphone&locale=en_US&tag= Phone#TI9

Additionally you can check your Do Not Disturb settings using this article:

iOS: Using Do Not Disturb

http://support.apple.com/kb/HT5463

Thanks for reaching out to Apple Support Communities.

Cheers,

Pedro.

Could it be that you are inadvertantly connected to a bluetooth device. My iPhone 5 was not ringing and I missed txts and then realised that I have bluetooth permanently on to use the handsfree in the car! Switched bluetooth off and all is good - but must admit that i did not have this problem pre the v7.1.1 upgrade.