Solution 1 Recover deleted iPhone notes from Gmail
Gmail email is a very common storing place for notes, usually you may have added your notes to the Gmail account without even knowing it. Because the first time when you sync your notes to iCloud, you should set a mail account. If you have set a Gmail account, the synced notes are actually stored as email in the notes label of your Gmail, which provides a possibility to restore iPhone notes from Gmail. Then just go to your Gmail to find back your deleted iPhone notes.
Solution 2 Recover deleted iPhone notes from iTunes Backup using iTunes
If you have synced or backed up your iPhone via iTunes, you can easily recover notes from iPhone by restoring iPhone from iTunes Backup. Because when you restore iPhone from iTunes backup, you restore the total iTunes backup data to your iPhone. Here are brief instructions for your reference.
Connect your device to the computer and run iTunes. When the connected device has been recognized by iTunes, click your device on the “Devices” column of the left sidebar, then you can see the Summary tab on the right, select Backups > This computer > Restore Backup…
Then choose a backup of your iPhone from the pop-up “Restore from Back up” window.
Please note that, to restore iPhone from iTunes backup in this way, not only your notes, but also all the other types of files in your previous backup will be restored, but they’ll overwrite and replace the current data on your iPhone.
Solution 3 Recover deleted iPhone notes from iCloud Backup
In order to recover deleted iPhone notes from iCloud backup, firstly you should make sure you have an iCloud backup by tapping Settings > iCloud > Storage & backup > manage storage space, then you can see the iCloud backup list of all your iOS devices.
After ensuring there’s an iCloud backup, you can refer to the short guide below about how to recover iPhone from iCloud backup.
On your iOS device, go to Settings > General > Software Update. You should update your device to the latest iOS, so you can restore from a recent backup of another device, such as a lost or broken device.
Go to Settings > General > Reset, then tap “Erase all content and settings”.
Then you’ll be led to the Setup Assistant, sign in to iCloud, tap “Restore from a Backup”, then choose from the list of your backups in iCloud.
Then all the data on your iCloud backup will be restored to your iPhone, including the iPhone notes. In Step 2 above, you must have noted that you have to remove all contents and settings on your iPhone device so as to recover deleted iPhone notes from iCloud backup.