Syncing old iMessages on new device

Hi KeithTP,

For help with iCloud for Messages, you can double-check all Text Message forwarding settings are correct on the iPhone with the help of the guide here, and details below: Set up iCloud for Messages on all your devices - Apple Support

"Set up iCloud for Messages on your iPhone, iPad, or iPod touch

1. On your iPhone, iPad, or iPod touch, go to Settings > [your name] > iCloud.
2. Do one of the following:

• iOS 16, iPadOS 16, or later: Tap Show All, tap Messages, then turn on Sync this [device].
  • 
  • iOS 15, iPadOS 15, or earlier: Turn on Messages.

Any messages currently stored in iCloud are now accessible on your device, and any new messages you receive on your device will be stored in iCloud.

3.To make sure you can see your messages on all your devices, also check the following:

• iMessage account: On your iPhone, iPad, or iPod touch, go to Settings > Messages > Send & Receive. Make sure that you’re signed in to iMessage with the same Apple ID. You can choose which email addresses and phone numbers you want to send and receive messages from on each device.
• Text message forwarding: If you want to receive SMS and MMS messages on all your devices, go to Settings > Messages > Text Message Forwarding on your iPhone. Turn on text message forwarding for each device. For more information, see the Apple Support article How to forward SMS/MMS text messages from your iPhone to your iPad, iPod touch or Mac.

4.To see messages stored in iCloud, open the Messages app."

Additionally, you may want to re-pair the Apple Watch with the new companion iPhone to make sure the data syncs as expected. How to pair your Apple Watch with a new iPhone - Apple Support

If you continue to have any issues, reach out to Apple Support to check on the account and further assist.

Contact - Official Apple Support

Contact Apple for support and service - Apple Support

Cheers.