Multi-page is a queue, not a magic feeder
You are the document feeder
Phones do not grab the next sheet. After each capture, put the next page down, shoot, add. If you skip a sheet, the PDF will too.
Check thumbnails like a copy clerk
Upside-down page 3 is cheaper to reshoot now than to explain later. Rotate before you export if the UI offers it.
When to merge instead
If you already have three PDFs from three evenings, concatenate with Merge PDF. This spoke is for photos of paper in one sitting.