Am I legally obligated to give the credit card company my cell number?

Received an email today from American Express, telling me that my cell phone number was missing, even though they have my home phone and my work phone numbers. (I have had that account for 30 years, probably, and there was no such thing as a cell phone when I opened it.)

Am I legally required to enter it?

I really don’t want to – it’s another data point that can be stolen if they are hacked. And in 30 years they have never called either of my other phone numbers. If there is something important, they can email me.