I currently have an Iphone. If i purchase the app and later get another phone that is not an Iphone, Do i have to purchase the app again for that that other phone?
Previously subscription entitlements were linked to specific app purchases (that is, the specific app IDs) so those purchases were only retrievable by restoring the purchase via the App Store.
Fortunately purchases today and past purchases are now linked to your login rather than your app purchase. What this means is that when you login using a third-party authentication provider such as Facebook or Google the entitlements will be blinded to those logins. That means if you sign in regardless of which platform drops is running the entitlement will be retrieved. I am using my Polyglot Plan entitlement (now known as Lifetime Premium Plan) on both Sndroid and iOS versions of Drops. So you no longer need to use the Restore Purchase function.
I think Drops has a one-time transition operation for past purchases so that when you restore your purchase you can then sign in (if you haven’t yet) and it will bind that purchase to your login. From there on you no longer need to use restore purchase, all you need to do is sign in