Short answer: before cleaning your phone, back up the things that would be hardest to recreate later. That usually means important photos, videos, documents, chat files, travel records, receipts, and anything tied to active work or upcoming plans.
This does not mean you need to back up every screenshot before a routine cleanup. The point is to protect the categories where wrong deletion would actually hurt, then clean the obvious clutter with less hesitation.
What is worth backing up first
Important personal photos and videos that do not exist anywhere else.
Documents, scans, receipts, and records tied to finances, work, or legal tasks.
Chat files or attachments you still rely on outside the app itself.
Travel bookings, tickets, confirmations, and active reference materials.
What usually does not need special backup first
Old screenshots, memes, and one-time reference images.
Obvious duplicate photos once you have chosen the keeper.
Low-value downloads and stale attachments you already know you do not need.
Why this makes cleanup easier
Backing up the highest-consequence categories first lowers the emotional risk of cleanup. Once that pressure is off, it becomes much easier to delete the obvious clutter in a sensible order instead of postponing the whole job.
If you want the next-step cleanup order after this, continue to Storage Full: What Should I Delete First?. If you want the broader route, open clean up phone storage.
The best pre-cleanup backup is not everything. It is the small set of things you would actually regret losing.