How to Combine Scanned Phone Photos Into One PDF
Phone scanner apps almost always save each page as a separate image or a separate single-page PDF — useful for capturing quickly, useless for actually sending a multi-page document as one file.
Why this happens
Scanner apps are built around a capture-one-page-at-a-time workflow, and most save each capture as its own file by default so you can review and retake individual pages before finalizing. Some apps do let you build a multi-page document within the app itself, but plenty of people scan pages individually, end up with a camera roll full of separate images, and then need to combine them after the fact.
The straightforward fix
Whether you've got several image files (JPG/PNG) or several single-page PDFs, the fix is the same: a merge tool that accepts both. Add the pages in the order they should appear — most tools let you drag to reorder afterward if you scanned out of sequence — and combine them into one PDF.
Getting the order right without renumbering files
You don't need to rename or renumber your files beforehand. Add them in whatever order they land, then reorder visually — dragging thumbnails is faster and less error-prone than trying to get filenames like scan_1.jpg, scan_2.jpg right, especially past scan_9.jpg where alphabetical and numerical sorting disagree.