Recover photos on mobile app

If you have the free app then you would need to restore from a back up of that old phone.

If you have a subscription, then the photos should appear if you have signed in with the correct account details

Are you logged into Lightroom on your phone with the same Adobe account? If so, all the images should be there in Lightroom exactly as on the old phone. If you had an of the Lightroom photos stored locally on the old phone, they are gone and you will have to go through the albums and start the local storage all over.