You mean to disable "SMS text messages as your 2FA", not delete your phone number associated with Coinbase (i forgot, but isn't a phone number needed for your Coinbase - as an identity or something?)
Two ways I researched to avoid this issue and keep your phone:
- Get a pre-paid phone (not associated with any identity)
- Google Voice number
if someone knows more about the subject, please feel free to comment...
Another thing to add.. It seems that nowadays everyone is using Gmail. Ok, i wonder, don't people use paid email providers? (like if you have your own domain ) or maybe in cryptoland that's way more transparent...
..... Now all other story is if you lose your phone or that physical key breaks (or is lost).......