Q: how do I retrieve an old back up from icloud on my new phone

Apple states that it keeps up to your most recent 3 backups (space permitting in your account).  If you're backing up daily, this would only go back a couple of days.  You won't know if an earlier backup is available until you attempt to back up to iCloud.  When you do, you are shown a list of available backups to restore from.  If you have older backups, you access those by tapping "Show older backups..." (see image below).  If you don't see this, you don't have any older backups available.