I want iphone photos numbered sequentially

We're not Apple. We're other users. You'll have to ask Apple for the change.

Scripting apps are something usually found on macOS or Windows, which is where various folks process and store and archive their images. Scripting is more of a slog on iPhone, where it's even possible. Scripting on macOS, much easier.

An iPhone app that might be useful here is Metapho, as that can reportedly batch-process EXIF data.

Log feedback with the folks at Apple.

Pending any potential changes to the file-naming in some future Apple software update, I suspect you'll be writing a script to rename the photos should sequential numbering be required. There are various ways to do bulk renames, and I'd be surprised if there weren't some scripts or tools around that can read and rename using EXIF data from the images.

Having just checked locally, the photos I've taken with the iPhone camera (iOS 13.7) are using sequential filenames, but photos from other apps and that have been edited have names all over. Photos from other sources have been getting odd names for a while now, too.

There is no such setting. That is why I both suggested feedback to Apple, and suggested work-arounds.

The photos under the photos tab are ordered sequentially. Recently added shows the photos as they were added, not when the picture was taken.

Oh ok. Apologies for misunderstanding. I have not personally messed with photos outside of photos and am not aware of a way to change the name of photos taken to make them sequential.