Lost Photos after subscription upgrade due to phone change

Your post suggests that until the phone change you were using the free version of Lightroom Mobile on the old phone, is that correct? Then in order to get your images from the old phone you decided to sign up for a subscription in order to sync the images from the old phone to the new phone? 

Assuming that's correct, did you sign up for the subscription on the old phone or the new phone. If it was on the old phone, did you then login to the LrM app on that phone and verified that you could still see all your photos? Then did you enable syncing in LrM on the same phone? If all that went smoothly, did you then keep the app open on the old phone for as long as it took to upload the photos to the cloud?

You'd probably need an Adobe Staff member to have a look from their end..

What phone are you using and do you have any back ups prior to the photos disappearing?

Often this is caused by incorrect log in details, so double check them.

Also, can you see any photos on Lightroom Web:

http://lightroom.adobe.com/. Photos would have  to sync to the cloud prior to syncing to you new phone.