Setting up a new iphone

You won’t lose information from the old phone; setting up a new phone is non-destructive, and won’t change anything on the old phone except that the phone number will be disabled and moved to the new phone.

Follow this guidance→Transfer data from your previous iOS or iPadOS device to your new iPhone or iPad - Apple Support

Your old phone is fine and the migration does not effect the old contents, but you undoubtedly also already have backups of your old iPhone too, right?

This because the only way to mark data as being important is with backups.

Without backups, we’re all one drop, one dunk, one error, one loss, one theft, one failure, away from data loss.