To find old Safari bookmarks (and avoid getting finger cramps from scrolling), use the search bar in the bookmark menu. On your iPhone, launch Safari and click the book icon. Then, swipe up to expand the list of bookmarks – you should find a search bar at the top. As long as you limit your bookmarks to 450 per folder, they won’t get deleted.
If you want to find deleted Safari bookmarks, you can use the “Restore Bookmarks” function in your Account Settings page on iCloud.com. Alternatively, use a data recovery software like Disk Drill.