I tried to upload an image I had taken at a rowing event to the event's album using my Samsung Z Flip 5 phone.  I was restricted to three sources: Camera | Camcorder | Voice Recorder

See attached. I found one topic about uploading images one by one from an iPhone but no chat about an android.

Have others had any success or know the tricks to making this work?

Second question: has anyone succeeded in uploading multiple images from their phones to an album, perhaps using an external integration?  Or are IPS users stuck with uploaded one image at a time, and .... only from an iPhone?!

Im not sure what it is you are asking here unfortunately. The button itself is just an upload button. What your device shows is up to the device itself

Here is the attachment I forgot to add.

why I click on camera, it just activates the camera.

 I am trying to reach out to the Invision Community that uses an Android phone and has encountered this issue, and find out if there is a work around or a setting to enable to upload images from say the phone gallery.  I realize most of the Invision Community staff uses an iPhone, except Esther, but perhaps others, those of us who are the 'outliers,' and use an Android phone, might be able to share what they do.

Yeah, what you are seeing there is related to the device rather than the site unfortunately. There may well be an android user here who can help, of course.