The SparkReceipt mobile app adds one document at a time: Take a photo, Select from gallery or Select from files each create a single document. If you have a backlog of receipt photos on your phone, use mass upload in the web app, which takes up to 100 files in one batch.
Option 1: use the web app in your phone's browser
Open app.sparkreceipt.com in your phone's browser and log in. Tap Add at the top of the page (or Add documents in the menu) and choose Upload many documents at once. Pick the photos from your camera roll, choose what to import them as under Import files into, and tap Start processing. The page is laid out for a computer screen, but it works on a phone.
Keep the page open until all the files have uploaded. After that, scanning continues on our servers and you can close the browser.
Option 2: move the photos to a computer first
For a larger backlog, it's usually quicker to copy the photos to your computer (for example with Google Drive, iCloud, AirDrop or a USB cable) and use mass upload there. You can drag and drop up to 100 files per batch.
The full walkthrough, including how long it takes and how to set a Category or Tags for the whole batch afterwards, is in How do I mass upload many receipts at once?
Sharing several photos to the app
You can also share photos from your phone's gallery to SparkReceipt with the share button. If you share several photos in one go, they are added as files of a single document, which is the right choice for a long receipt photographed in parts but not for separate receipts. Share separate receipts one at a time, or use mass upload. See Can I send receipts to SparkReceipt from WhatsApp, a scanner or other apps?