IOS – Why is the iPhone label available on some contacts but not others on the iPhone 5S

A custom label will have to suffice here. I have many contacts with their cell phones listed as 'mobile', and then a custom 'Google Voice' labeled number.

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An alternative to this is to make the change via Address Book.app on your computer, then sync the contacts to your phone.

Custom labels are available in all contact adding/modification screens.

First, browse to a contact, and tap the label name (to the left of a phone number, e-mail address, etc.). You will see the list of labels.

Second, swipe all the way to the bottom, and tap on "Add Custom Label".

Type in a new Custom Label;

And then it will be displayed next to the number.

It will now appear in a list of custom labels on later access.

Believe it or not, this is often a minor activation issue–assuming the iPhone is on Sprint or Verizon. On Verizon, Dial *228 from the Phone app. On Sprint, dial ##UPDATE# (##873283#). Follow the voice prompts, if any. The process takes a minute or two. After you get a pop-up message indicating the update was successful, wait another minute. You should see your service indicator go away for a moment then come back.

Afterward, try Siri again. This will likely resolve your text message issues too, though a restart of the iPhone (hold sleep/wake button, swipe to shut off, wait, start back up) may be necessary there.