I used to have Spotify Premium but after I change a new iPhone and download Spotify again, I do not have it any more. I use the e-mail which is used to sign up to find back my username. And I login use this username, but still do not have the Premium.
welcome to the community!
If you only changed phones and didn't change plans you should still have access to your Spotify premium account. Are you sure you have the right username? I once created my free version with my Facebook account and created a different username using my Premium account.
Let us know how it goes.