applying custom labels to contacts

Do you mean the labels where you customize e.g. ‘home’/‘work’/‘other’/etc. for some other description? Picking ‘other’ is not enough: you have to select Add Custom Label, or select from a previously used label below that.

Or do you mean adding fields? They do often not appear near the bottom, where you press ‘add field’, most appear near the top, where the name info is. The field will disappear again if left empty, when you exit Edit mode. Could that be it?

Open Contacts app

Open the contact where you need to add a custom label

Tap Edit (top-right)

Tap on the existing label, then scroll down to Add Custom Label and write it.

Tap Done (top-right)

If you still can't do it, force restart your iP6s (Press and hold both the Home and the Power (or Side) buttons for at least 10 seconds, until you see the Apple logo. When it appears, release both buttons, wait for your iphone to restart.)

Repeat all the steps provided.

If your profile is OK, your iphone is not updated to the latest iOS version (11.3). We always suggest to run the most recent IOS also because of security patches that are included in almost every new version.

Regards

Giulio

From you last post, as Idris suggested, the issue could be related to the Exchange account (settings? configuration? ActiveSync?). I don't use Exchange, so I'm not competent enough to offer you an appropriate explanation.

On my iP7, using Gmail and/or iCloud e-mail accounts, I can easily change / add custom labels on each contact I have.

Please keep us informed.

Thanks and regards

Giulio

If you're using an Exchange account, you may be limited to the labels provided by Exchange account.