Are you a paid user? If so, Lightroom Mobile should have synced images on your old device to Lightroom cloud storage, and thes should appear on your new device.
If you are using the free version of Lightroom Mobile, images are kept only on the device and do not sync to cloud storage , and so the images will not appear on other devices even when you sign into the same account. In this scenario, the easiest way to restore your images is to make a backup of your old phone, and restore that backup onto your new device.
Another option: on your old device, in Lightroom check the in-app purchase screen to see if a 7-day Free Trial is offered. If so, perhaps you can use the free trial period to sync your images with edits to Lightroom's cloud storage, and signing in on your new device you should see all the same files appear in the same account. Just be sure to cancel before the free 7-day trial ends if you don't want to keep cloud sync/backup going.