Question: how do you change your voicemail on your iphone?
Answer: From a Home screen, tap the Phone app .
Tap Voicemail. then tap Greeting (upper-left). ... 
Tap Custom to record a greeting. Enabled when a checkmark is present.
Tap Record to begin recording the custom greeting message. To listen to your recording before saving, tap Stop then Play.
Tap Stop to end recording then tap Save.