I changed my phone for a samsung and when I sync my anki on the app, it downloads the cards all over again and it takes a long time. Is there a way to fix that?
For the very first sync, make sure to sync when your phone is connected via WiFi to a fast internet connection, rather than over a mobile network;
If there is a heavy deck which you don’t want, remove that big deck before syncing (using ankiweb, or using the desktop version and syncing after deleting the deck); or you can make a new profile with fewer decks;
Download the decks separately as .apkg files rather than by syncing (again, make sure to do that over a fast internet connection, not a mobile network); note that this will probably cause a conflict the next time you sync, but when resolving the conflict, Anki should only download the notes, not the media, so it should be much faster)