Could this be used to hang off a golf bag and hold an iPhone? and where on the bag could this hang?

Yes. It's pretty sturdy holding the phone and you can tighten it on where you insert your clubs.

Can you use on a wheelchair it’s strong?

Yes, It's very strong.

Will it clamp on a round bar? Like a pipe?

Yes, It can clamp on a round pipe.

Is this useful to hold a phone to act as a doc cam?

Yes, it’s sturdy and won’t drop down over time.

Can this hold my iphone face down? objective is keep iphone stable while i scan multiple pages to pdf.

Yes, it holds a phone very securely in that position.