My iphone 5 does not ring or provides text alerts when in locked mode. Any reasons?

Do you not get any rings at all? I'd check if your do not disturb mode is on

Under Settings check Do Not Disturb:

• Choose Manual to turn on Do Not Disturb or Swipe up from the bottom of the screen to open Control Center. Tap the crescent moon.
• If it is the Manual setting is on (and the crescent moon appears, then you will not hear alerts when locked.
• Turn it off and you'll hear alerts when the phone is locked